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Research about Arizona, California

Source-linked reports with geographic coverage including Arizona, California.

At least 37 records · Page 2Linked to original sources
USGS2017

Satellite-based water use dynamics using historical Landsat data (1984–2014) in the southwestern United States

Remote sensing-based field-scale evapotranspiration (ET) maps are useful for characterizing water use patterns and assessing crop performance. The relative impact of climate variability and water management decisions are better studied and quantified using historical data that are derived using a set of consistent datasets and methodology. Historical (1984–2014) Landsat-based ET maps were generated for major irrigation districts in California, i.e., Palo Verde and eight other sub-basins in parts of the middle and lower Central Valley. A total of 3396 Landsat images were processed using the Operational Simplified Surface Energy Balance (SSEBop) model that integrates weather and remotely sensed images to estimate monthly and annual ET within the study sites over the 31 years. Model output evaluation and validation using gridded-flux data and water balance ET approaches indicated relatively good correspondence (R 2 up to 0.88, root mean square error as low as 14 mm/month) between SSEBop ET and validation datasets. In a pairwise comparison, annual variability of agro-hydrologic parameters of actual evapotranspiration ( ET a ), land surface temperature ( T s ), and runoff ( Q ) were found to be more variable than their corresponding climatic counterparts of atmospheric water demand ( ET o ), air temperature ( T a ), and precipitation ( P ), revealing process differences between regional climatic drivers and localized agro-hydrologic responses. However, only T a showed a consistent increase (up to 1.2 K) over study sites during the 31 years, whereas other climate variables such as ET o and P showed a generally neutral trend. This study demonstrates a useful application of “Big Data” science where large volumes of historical Landsat and weather datasets were used to quantify and understand the relative importance of water management and climate variability in crop water use dynamics in regards to the linkages among water management decisions, hydrologic processes and economic transactions. Irrigation district-wide ET a estimates were used to compute historical crop water use volumes and monetary equivalents of water savings for the Palo Verde Irrigation District (PVID). During the peak crop fallowing year in PVID, the water saved reached a maximum of ~ 107,200 acre-feet in 2011 with an estimated monetary payout value of $20.5 million. A significant decreasing trend in actual ET despite an increasing atmospheric demand in PVID highlights the role of management decisions in affecting local hydrologic processes. This study has importance for planning water resource allocation, managing water rights, sustaining agricultural production, and quantifying impacts of climate and land use/land cover changes on water resources. With increased computational efficiency, similar studies can be conducted in other parts of the world to help policy and decision makers understand and quantify various aspects of water resources management.

Arizona, California↗
USGS2013

Geologic map of the Topock 7.5’ quadrangle, Arizona and California

The Topock quadrangle exposes a structurally complex part of the Colorado River extensional corridor and also exposes deposits that record landscape evolution during the history of the Colorado River. Paleoproterozoic gneisses and Mesoproterozoic granitoids and intrusive sheets are exposed through tilted cross-sectional thicknesses of many kilometers. Intruding them are a series of Mesozoic to Tertiary igneous rocks including dismembered parts of the Late Cretaceous Chemehuevi Mountains Plutonic Suite. Plutons of this suite in Arizona, if structurally restored for Miocene extension, formed cupolas capping the Chemehuevi Mountains batholith in California. Thick (1–3 km) Miocene sections of volcanic rocks, sedimentary breccias, conglomerate, and sandstone rest nonconformably on the Proterozoic rocks and record the structural and depositional evolution of the Colorado River extensional corridor. Four major Miocene low-angle normal faults and a steep block-bounding fault that developed during this episode divide the deformed rocks of the quadrangle into major structural plates and tilted blocks in and east of the Chemehuevi Mountains core complex. The low-angle faults attenuate crustal section, superposing supracrustal and upper crustal rocks against gneisses and granitoids originally from deeper crustal levels. The transverse block-bounding Gold Dome Fault Zone juxtaposes two large hanging-wall blocks, each tilted 90°, and the fault zone splays at its tip into folds in layered Miocene rocks. A synfaulting intrusion occupies the triangular zone where the folded strata detached from an inside corner along this fault between the tilt blocks. Post-extensional upper Miocene to Quaternary strata, locally deformed, record post-extensional landscape evolution, including several Pliocene and younger aggradational episodes in the Colorado River valley and intervening degradation episodes. The aggradational sequences include (1) the Bouse Formation, (2) fluvial deposits correlated with the alluvium of Bullhead City, (3) the younger fluvial boulder conglomerate of Bat Cave Wash, (4) the fluvial Chemehuevi Formation and related valley-margin deposits, and (5) fluvial Holocene deposits under the river and the valley floor. These fluvial records of Colorado River deposition are interspersed with piedmont alluvial fan deposits of several ages.

Arizona, California↗
USGS2012

An axial view of a metamorphic core complex: Crustal structure of the Whipple and Chemehuevi Mountains, southeastern California

A 135‐km‐long, NW‐SE trending, seismic refraction/wide‐angle reflection profile provides a unique along‐strike view of the crustal structure of a belt of metamorphic core complexes in southeastern California: the Whipple, Chemehuevi, and Sacramento mountains metamorphic core complexes. Interpretation of the seismic data was done by two‐dimensional forward modeling of travel times and amplitudes. The final model consists of (1) a thin (< 1.5 km) veneer of upper plate and fractured lower plate rocks (velocities of 1.5–5.3 km s −1 ) overlying a fairly homogeneous basement with velocities of 6.0 km s −1 ; (2) a localized, high‐velocity (6.4 km s −1 ) body, situated directly beneath the Whipple Mountains; (3) a 6.3–6.4 km s −1 middle crust that is thickest beneath the core complexes; (4) a 6.65±0.15 km s −1 lower crust; (5) crustal thickness of 27 km with a deeper crustal root (3 km) beneath the Whipple Mountains metamorphic core complex; and (6) a P n velocity of 8.0±0.10 km s −1 . The crustal structure that underlies the belt of metamorphic core complexes provides new insights into the processes that control extension in the deep crust. Upper crustal velocities are higher beneath the Whipple Mountains (where velocities increase to 6.4 km s −1 at ∼5 km depth) than beneath the Chemehuevi and Sacramento mountains. In addition, midcrustal discontinuities rise 2–5 km beneath the Whipple complex compared to the other complexes. These observations support greater uplift and a slightly deeper midcrustal origin for the rocks now exposed in the core of the Whipple Mountains compared to rocks in the Chemehuevi and Sacramento mountains. Despite the enhanced uplift and extension in the Whipple Mountains, the crust is thicker here (30 km) than anywhere else along the Colorado River extensional corridor. This may be in part a relic of compressional and magmatic thickening during the Mesozoic. However, we suggest that inflation of the crust during Tertiary extension was the dominant mechanism. Both mantle‐derived magmatism and lateral ductile inflow in the crust are proposed.

Arizona, California↗
USGS2012

Tertiary basin development and tectonic implications, Whipple Detachment System, Colorado River Extensional Corridor, California and Arizona

Colorado River extensional corridor. In the Mohave Mountains and Aubrey Hills of Arizona and the eastern Whipple Mountains of California near Parker Dam, these deposits comprise four unconformity-bounded sequences composed of locally derived epiclastic and volcanic rocks and the Peach Springs Tuff. The three older sequences represent syntectonic units that were deposited coeval with detachment faulting, and the fourth is interpreted to be postextensional. The sequences are correlated between four fault-bounded regions, which are the remnants of four different depositional basins. Similar sequences can be correlated over broad areas of the extensional corridor despite the general lack of widespread units. The basins developed in about the same positions, relative to each other and to volcanic sources, as they occupy at present. This is shown by gradational changes of pre-Tertiary rock types between regions, systematic variations in the abundance of magmatic units, and correlative volcanic units that occur in two adjacent regions. The basins formed in the early Miocene from segmentation of the upper crust into blocks bounded by high-angle faults that trended both parallel and perpendicular to the direction of extension and which were terminated at middle crustal depths by a low-angle detachment fault. Extreme rotation of one large crustal block, which constitutes the central Mohave Mountains, is recorded by a major unconformity in the lower Miocene section of one basin. Because coeval sections that formed in adjoining basins do not record this rotation, the underlying crustal blocks must have been separated by transfer faults that allowed them to rotate independently. These proposed transfer faults are represented at present by major faults with trends that parallel the direction of extension on the Whipple detachment system.

Arizona, California↗
USGS2012

Postfire chaparral regeneration under mediterranean and non-mediterranean climates

This study compares postfire regeneration and diversity patterns in fire-prone chaparral shrublands from mediterranean (California) and non-mediterranean-type climates (Arizona). Vegetation sampling was conducted in tenth hectare plots with nested subplots for the first two years after fire. Floras in the two regions were compared with Jaccard's Index and importance of families and genera compared with dominance-diversity curves. Although there were 44 families in common between the two regions, the dominant families differed; Poaceae and Fabaceae in Arizona and Hydrophyllaceae and Rosaceae in California. Dominance diversity curves indicated in the first year a more equable distribution of families in Arizona than in California. Woody plants were much more dominant in the mediterranean climate and herbaceous plants more dominant in the bimodal rainfall climate. Species diversity was comparable in both regions at the lowest spatial scales but not at the tenth hectare scale. Due to the double growing season in the non-mediterranean region, the diversity for the first year comprised two different herbaceous floras in the fall and spring growing seasons. The Mediterranean climate in California, in contrast, had only a spring growing season and thus the total diversity for the first year was significantly greater in Arizona than in California for both annuals and herbaceous perennials. Chaparral in these two climate regimes share many dominant shrub species but the postfire communities are very different. Arizona chaparral has both a spring and fall growing season and these produce two very different postfire floras. When combined, the total annual diversity was substantially greater in Arizona chaparral.

Arizona, California↗
USGS2012

Groundwater quality in the Colorado River basins, California

Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of California created the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The Priority Basin Project of the GAMA Program provides a comprehensive assessment of the State’s groundwater quality and increases public access to groundwater-quality information. Four groundwater basins along the Colorado River make up one of the study areas being evaluated. The Colorado River study area is approximately 884 square miles (2,290 square kilometers) and includes the Needles, Palo Verde Mesa, Palo Verde Valley, and Yuma groundwater basins (California Department of Water Resources, 2003). The Colorado River study area has an arid climate and is part of the Sonoran Desert. Average annual rainfall is about 3 inches (8 centimeters). Land use in the study area is approximately 47 percent (%) natural (mostly shrubland), 47% agricultural, and 6% urban. The primary crops are pasture and hay. The largest urban area is the city of Blythe (2010 population of 21,000). Groundwater in these basins is used for public and domestic water supply and for irrigation. The main water-bearing units are gravel, sand, silt, and clay deposited by the Colorado River or derived from surrounding mountains. The primary aquifers in the Colorado River study area are defined as those parts of the aquifers corresponding to the perforated intervals of wells listed in the California Department of Public Health database. Public-supply wells in the Colorado River basins are completed to depths between 230 and 460 feet (70 to 140 meters), consist of solid casing from the land surface to a depth of 130 of 390 feet (39 to 119 meters), and are screened or perforated below the solid casing. The main source of recharge to the groundwater systems in the Needles, Palo Verde Mesa, and Palo Verde Valley basins is the Colorado River; in the Yuma basin, the main source of recharge is from subsurface flow from the groundwater basins to the west. Groundwater discharge is primarily to pumping wells, evapotranspiration, and, locally, to the Colorado River.

Arizona, California↗
USGS2011

Unravelling long-term vegetation change patterns in a binational watershed using multitemporal land cover data and historical photography

A significant amount of research conducted in the Sonoran Desert of North America has documented, both anecdotally and empirically, major vegetation changes over the past century due to human land use activities. However, many studies lack coincidental landscape-scale data characterizing the spatial and temporal manifestation of these changes. Vegetation changes in a binational (USA and Mexico) watershed were documented using a series of four land cover maps (1979-2009) derived from multispectral satellite imagery. Cover changes are compared to georeferenced, repeat oblique photographs dating from the late 19 th century to present. Results indicate the expansion of grassland over the past 20 years following nearly a century of decline. Historical repeat photography documents early-mid 20 th century mesquite invasions, but recent land cover data and rephotography demonstrate declines in xeroriparian/riparian mesquite communities in recent decades. These vegetation changes are variable over the landscape and influenced by topography and land management.

Arizona, California↗
USGS2009

Geologic Map of the Needles 7.5' quadrangle, California and Arizona

The Needles 7.5' quadrangle straddles the Colorado River in the southern part of the Mohave Valley, in Mohave County, Arizona, and San Bernardino County, California. The quadrangle contains part of the Havasu National Wildlife Refuge, sections of the Fort Mojave Indian Reservation, most of the city of Needles, and several major interstate highways and railroads. The quadrangle is underlain by structurally undeformed sediments of Pliocene and younger age that were deposited by the Colorado River, as well as alluvial fan deposits on the piedmonts that flank the Black Mountains (in Arizona) and the Sacramento Mountains (in California). Multiple cycles of aggradation of the Colorado River, each followed by episodes of downcutting, are recorded by Pliocene through historic deposits on the piedmonts that border the floodplain. Regionally, the complex stratigraphy related to the Colorado River has been the subject of geologic interest for over 150 years. The California and Arizona piedmont portions of the Needles quadrangle expose a subset of this incompletely understood stratigraphic record. Thus, the stratigraphic sequence presented on this map is a version of the stratigraphy of the Colorado River as interpreted locally. The deposits in the recently active Colorado River valley floor support riparian habitat and irrigated agriculture. The distributions of sand-rich channel deposits and mud-rich floodplain deposits in the valley are mapped on the basis of the history of the movement of the Colorado River in the quadrangle, which has been documented in sequential aerial photographs since 1937 and maps dating to 1857.

Arizona, California↗
USGS2008

Wide-area estimates of saltcedar (Tamarix spp.) evapotranspiration on the lower Colorado River measured by heat balance and remote sensing methods

In many places along the lower Colorado River, saltcedar ( Tamarix spp) has replaced the native shrubs and trees, including arrowweed, mesquite, cottonwood and willows. Some have advocated that by removing saltcedar, we could save water and create environments more favourable to these native species. To test these assumptions we compared sap flux measurements of water used by native species in contrast to saltcedar, and compared soil salinity, ground water depth and soil moisture across a gradient of 200–1500 m from the river's edge on a floodplain terrace at Cibola National Wildlife Refuge (CNWR). We found that the fraction of land covered ( f c ) with vegetation in 2005–2007 was similar to that occupied by native vegetation in 1938 using satellite-derived estimates and reprocessed aerial photographs scaled to comparable spatial resolutions (3–4 m). We converted f c to estimates of leaf area index (LAI) through point sampling and destructive analyses ( r 2 = 0·82). Saltcedar LAI averaged 2·54 with an f c of 0·80, and reached a maximum of 3·7 with an f c of 0·95. The ranges in f c and LAI are similar to those reported for native vegetation elsewhere and from the 1938 photographs over the study site. On-site measurements of water use and soil and aquifer properties confirmed that although saltcedar grows in areas where salinity has increased much better than native shrubs and trees, rates of transpiration are similar. Annual water use over CNWR was about 1·15 m year −1 .

Arizona, California↗
USGS2008

Magmatism and tectonics in a tilted crustal section through a continental arc, eastern Transverse Ranges and southern Mojave Desert

This field guide describes a two-and-one-half day transect, from east to west across southern California, from the Colorado River to the San Andreas fault. Recent geochronologic results for rocks along the transect indicate the spatial and temporal relationships between subarc and retroarc shortening and Cordilleran arc magmatism. The transect begins in the Jurassic(?) and Cretaceous Maria retroarc fold-and-thrust belt, and continues westward and structurally downward into the Triassic to Cretaceous magmatic arc. At the deepest structural levels exposed in the southwestern part of the transect, the lower crust of the Mesozoic arc has been replaced during underthrusting by the Maastrichtian and/or Paleocene Orocopia schist.

Arizona, California↗
USGS2007

Status and habitat use of the California black rail in the Southwestern USA

California black rails ( Laterallus jamaicensis coturniculus ) occur in two disjunct regions: the southwestern USA (western Arizona and southern California) and northern California (Sacramento Valley and the San Francisco Bay area). We examined current status of black rails in the southwestern USA by repeating survey efforts first conducted in 1973–1974 and again in 1989, and also examined wetland plant species associated with black rail distribution and abundance. We detected 136 black rails in Arizona and southern California. Black rail numbers detected during past survey efforts were much higher than the numbers detected during our more intensive survey effort, and hence, populations have obviously declined. Plants that were more common at points with black rails included common threesquare ( Schoenoplectus pungens ), arrowweed ( Pluchea sericea ), Fremont cottonwood ( Populus fremontii ), seepwillow ( Baccharis salicifolia ), and mixed shrubs, with common threesquare showing the strongest association with black rail presence. Plant species and non-vegetative communities that were less common at points with black rails included California bulrush ( Schoenoplectus californicus ), southern cattail ( Typha domingensis ), upland vegetation, and open water. Black rails were often present at sites that had some saltcedar ( Tamarix ramosissima ), but were rarely detected in areas dominated by saltcedar. We recommend that a standardized black rail survey effort be repeated annually to obtain estimates of black rail population trends. Management of existing emergent marshes with black rails is needed to maintain stands of common threesquare in early successional stages. Moreover, wetland restoration efforts that produce diverse wetland vegetation including common threesquare should be implemented to ensure that black rail populations persist in the southwestern USA.

Arizona, California↗
USGS2007

Stratigraphy of Colorado River deposits in lower Mohave Valley, Arizona and California

Deposits in lower Mohave Valley and upper Topock Gorge near Topock, Arizona and Park Moabi, California record a succession of depositional and erosional events since late Miocene time that relate to the development of the Colorado River. Upper Miocene alluvial fans were deposited toward a depocenter east of the present valley bottom, indicating there was no valley outlet then through the area of Topock Gorge. The lower Pliocene Bouse Formation subsequently accumulated to thicknesses of at least 330 m in ancestral Mohave Valley before most of it was incised by a Colorado River that carried clasts as large as 0.9 m and drained southward through ancestral Topock Gorge. Pliocene fluvial sandstone and conglomerate exposed in this area record 160 m of subsequent aggradation. One or more sedimentary sequences of varied fluvial, paludal, and alluvial fan environments accumulated on the margin of the floodplain in Pleistocene time, including during deposition of the upper Pleistocene Chemehuevi Formation of Longwell (1936). River boulders as large as 1.2 m derived from Pliocene gravel were deposited in terraces along the river during later incision. Vertebrate fossil finds and historical descriptions of the 19th century enrich the history of the area

Arizona, California↗
USGS2007

Overview: The Chemehuevi Formation along the lower Colorado River

A distinctive set of fine-grained deposits occurs throughout the lower Colorado River Valley, extending from just below the mouth of Grand Canyon to well into the river delta below Yuma, AZ (Figure 1), an along-channel distance of over 700 km. Upstream of Parker, Arizona, the deposits consist of scattered erosional remnants up to 150 m above the modern floodplain. Below Parker, they occur in isolated outcrops but also underlie large continuous terraces such as Parker Mesa, Palo Verde Mesa, and Yuma Mesa. These deposits form the Chemehuevi Formation of Longwell (1936).

Arizona, California↗
USGS2006

Database for the east half of "Preliminary Geologic Map of the Blythe 30' by 60' quadrangle, California and Arizona"

This digital map database was prepared from the published Preliminary Geologic Map of the Blythe 30' by 60' Quadrangle, California and Arizona (U.S. Geological Survey Open-File Report 90-497). This database represents the east half of the original published map. The database contains exactly the same scientific content as the original map; no data have been added to, subtracted from, or modified from the original map. Like the original paper map, this database represents the general distribution of bedrock and surficial deposits in the mapped area. It provides information on the geologic structure and stratigraphy of the area covered. The database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U.S. Geological Survey. The scale of the original published map limits the spatial resolution (scale) of the database to 1:100,000 or smaller.

Arizona, California↗
USGS2006

Hydrogeologic framework refinement, ground-water flow and storage, water-chemistry analyses, and water-budget components of the Yuma area, southwestern Arizona and southeastern California

The ground-water and surface-water system in the Yuma area in southwestern Arizona and southeastern California is managed intensely to meet water-delivery requirements of customers in the United States, to manage high ground-water levels in the valleys, and to maintain treaty-mandated water-quality and quantity requirements of Mexico. The following components in this report, which were identified to be useful in the development of a ground-water management model, are: (1) refinement of the hydrogeologic framework; (2) updated water-level maps, general ground-water flow patterns, and an estimate of the amount of ground water stored in the mound under Yuma Mesa; (3) review and documentation of the ground-water budget calculated by the Bureau of Reclamation, U.S. Department of the Interior (Reclamation); and (4) water-chemistry characterization to identify the spatial distribution of water quality, information on sources and ages of ground water, and information about the productive-interval depths of the aquifer. A refined three-dimensional digital hydrogeologic framework model includes the following hydrogeologic units from bottom to top: (1) the effective hydrologic basement of the basin aquifer, which includes the Pliocene Bouse Formation, Tertiary volcanic and sedimentary rocks, and pre-Tertiary metamorphic and plutonic rocks; (2) undifferentiated lower units to represent the Pliocene transition zone and wedge zone; (3) coarse-gravel unit; (4) lower, middle, and upper basin fill to represent the upper, fine-grained zone between the top of the coarse-gravel unit and the land surface; and (5) clay A and clay B. Data for the refined model includes digital elevation models, borehole lithology data, geophysical data, and structural data to represent the geometry of the hydrogeologic units. The top surface of the coarse-gravel unit, defined by using borehole and geophysical data, varies similarly to terraces resulting from the down cutting of the Colorado River. Clay A is nearly the same as the previous conceptual hydrogeologic model definition (Olmsted and others, 1973), except for a minor westward extension from the city of Yuma. Clay B is extended to the southerly international boundary and increased in areal extent by about two-thirds of the original extent (Olmsted and others, 1973). The other hydrogeologic units generally are the same as in the previous conceptual hydrogeologic model. Before development, the Colorado and Gila Rivers were the sources of nearly all the ground water in the Yuma area through direct infiltration of water from river channels and annual overbank flooding. After construction of upstream reservoirs and clearing and irrigation of the floodplains, the rivers now act as drains for the ground water. Ground-water levels in most of the Yuma area are higher now than they were in predevelopment time. A general gradient of ground-water flow toward the natural discharge area south of the Yuma area still exists, but many other changes in flow are evident. Ground water in Yuma Valley once flowed away from the Colorado River, but now has a component of flow towards the river and Mexicali Valley. A ground-water mound has formed under Yuma Mesa from long-term surface-water irrigation; about 600,000 to 800,000 acre-ft of water are stored in the mound. Ground-water withdrawals adjacent to the southerly international boundary have resulted in water-level declines in that area. The reviewed and documented water budget includes the following components: (1) recharge in irrigated areas, (2) evapotranspiration by irrigated crops and phreatophytes, (3) ground-water return flow to the Colorado River, and (4) ground-water withdrawals (including those in Mexicali Valley). Recharge components were calculated by subtracting the amount of water used by crops from the amount of water delivered. Evapotranspiration rates were calculated on the basis of established methods, thus were appropriate for input to the ground-water flow model developed by the Bureau of Reclamation (William Greer, hydrologist, Bureau of Reclamation, written commun., 2005). Evapotranspiration by crops and phreatophytes were calculated by using crop coefficient methods and meteorological data. Other methods of calculating evapotranspiration rates by using combinations of satellite imagery and ground-based data could be used for higher spatial and temporal resolution. Ground-water return flow during years of low flow on the Colorado River (1972–82, 1987–92, and 1994–96) averaged 79,000 acre-ft per year. Ground-water withdrawal data for 1970–99 were similar to other estimates made by the U.S. Geological Survey for the Yuma area. New water-chemistry data were collected in 12 wells and 8 canals/drains to characterize spatial patterns in chemical constituents, determine isotopic ages of water, infer possible sources of ground water, and locate the vertical intervals of the aquifer that contribute most water to wells. Depth-dependent samples were collected at one of the wells (YM-10). A large quantity of water-quality data were compiled from Bureau of Reclamation and U.S. Geological Survey records and merged into the U.S. Geological Survey National Water Information System database. New samples were analyzed for major ions, nutrients, stable isotopes of oxygen and hydrogen, tritium ( 3 H), and carbon-14 ( 14 C) (along with C 13 /C 12 ratios). Light values of oxygen-18 ( 18 O) and deuterium ( 2 H, D) in well 242-2 indicate recharge from the Colorado River. Heavy water samples from wells 242-22, CADC, and Mesa del Sol indicate local recharge sources. Tritium data indicate there is young water in wells in the valleys and near the edge of Yuma Mesa, while older water is found far from the Colorado River. 14 C data indicate that water from wells near the southerly international boundary is at least several thousand years old.

Arizona, California↗