Geology topics

Research about Riverside County, California

Source-linked reports with geographic coverage including Riverside County, California.

39 records · Page 3Linked to original sources

USGS1976

Geohydrology of the Anza-Terwilliger area, Riverside County, California

The Anza-Terwilliger area consists of about 96 square miles (24-9 square kilometres) in the upper parts of the Santa Margarita River and Coyote Creek drainage basins in Riverside County, Calif., about 90 miles (145 kilometres) southeast of Los Angeles. This report deals with geology, steady state and transient state of ground water, net depletion of ground water, surface-water flow, precipitation, chemistry of water, land and water use, and gravity data for the Anza-Terwilliger area. The data indicate that the rate of ground-water depletion ha's accelerated since 1950. Pumping depressions adjacent to the Cahuilla Indian Reservation have increased the hydraulic gradient and are.causing water beneath the reservation to flow toward these depressions. Total depletion of ground water since 1950 is about 14,000 acre-feet (17.3 cubic hectometres). Chemical analyses indicate that the ground water in local areas contains concentrations of nitrate above that recommended by the Environmental Protection Agency for human consumption.

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USGS1976

Land subsidence and aquifer-system compaction in the San Jacinto Valley, Riverside County, California - A progress report

Widespread subsidence continues in the San Jacinto structural trough as water levels continue to decline. Subsidence is due principally to the compaction of water-bearing deposits as effective stresses are increased by artesian-head decline. Other possible contributory causes of subsidence are (1) local or regional tectonic adjustments and graben downfaulting, (2) natural compaction of deep water-bearing deposits below the bottom of well casings, and (3) continuing compaction of surficial deposits due to causes other than artesian-head decline. A careful analysis of 4 yr of correlative records of waterlevel, extensometer, and land-surface changes suggests three types of vertical ground movement occurring at the 4S/1W-21N2 recorder site near the San Jacinto reservoir site. The reservoir was drained in October 1973. Listed in descending order of magnitude these are (1) an elastic undulation of the land surface of about 0.06 ft (0.02 m) per year in close response to the roughly 50 ft (15 m) of seasonal water-level fluctuations, (2) a long-term permanent compaction of the deposits in the 0-1,237-ft (0-377-m) zone of about 0.04 ft (0.01 m) per year, and (3) a deep settlement of deposits below the 1,237-ft (377-m) extensometer anchor of 0.01-0.02 ft (0.003-0.006 m) per year, probably caused by continuing downfaulting in the graben trough. The specific compaction of the aquifer system at this site from 1970 to 1974 was about 1.3x 10 -2 (units of compaction per unit of increase in applied stress). The specific, expansion during this period decreased progressively from 1.29x 10 -3 (units of expansion per unit of stress decrease) in 1970-71 to 0.95x10 -3 in 1973-74, suggesting that excess pore pressures in the slow-draining aquitards were not completely dissipated each year.

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USGS1963

Hydrologic and geologic reconnaissance of Pinto Basin, Joshua Tree National Monument, Riverside County, California

Pinto basin, in the north-central part of Riverside County, Calif., is a typical desert valley formed by downfaulting along several major fault zones. The valley is filled with alluvium, and ground water in the alluvium discharges as subsurface outflow through an alluvium-filled gap at the east end of the valley. Occasionally surface water from cloudburst floods also discharges in a wash through the gap at the east end of the valley. A northeastward extension of the major fault along the south side of the valley acts as a barrier to the discharge of ground water from the valley. The average ground-water gradient is less than 1 foot per mile across the main part of the valley above this barrier, but the water level drops abruptly across the fault. The ground-water storage capacity of the uppermost 100 feet of saturated alluvium beneath the central valley area is estimated to be about 230,000 acre-feet. All this water in storage occurs at depths greater than 95 feet below the land surface and cannot be reached by plants or animals. During 1959 virtually all the water pumped in the area was withdrawn from storage. However, the quantity of water pumped is small in relation to the total quantity in storage. Except for a small decline in head, no evidence indicates that the pumping will greatly impair the yield for many years or cause the water to deteriorate in quality.

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