Tectonic setting of the San Diego formation aquifer,considered for conjunctive use storage

A number of alluvial aquifers in coastal southern California are either in current use or are being considered for aquifer storage and recovery (ASR). This conjunctive-use strategy involves artificial recharge with local or imported potable water or recycled water during low-use periods and extraction during high-use periods. Most of the aquifers are alluvial fill of eroded stream channels or are alluvial fill of actively subsiding tectonic basins in the Transverse Ranges geomorphic province. In both cases, the aquifer material is relatively tectonically undisturbed since deposition, and in many cases, individual aquifer units have considerable areal extent. The San Diego Formation aquifer, which spans the international border between Alta California and Baja California, is an exception. It was deposited in a pull-apart basin in the strike-slip regime of the Rose Canyon fault zone and parallel faults, which form the boundary between the Peninsular Ranges and Continental Borderlands geomorphic provinces. The formation has been faulted, internally fractured, and locally chemically altered. The lack of continuity of individual aquifer units that is observed in aquifer studies may be associated with localized patterns of syntectonic deposition.