WIRE, JEREMY C., JOHN K. HOFER, and KEIL A. ALBERT, Geoconsultants, Inc., San Jose, CA

Abstract: Pleistocene Deposition and Deep Aquifer Development in the Marin-Castroville Area, Monterey County, California

Test drilling and geophysical surveys to evaluate the potential of deeper aquifers below the 400-foot aquifer of local usage, reveal the presence of fresh-water bearing deposits extending to depths of at least 2,020 feet within portions of the study area. These deposits, which are designated as the 900-foot and 1,500-foot aquifers, consist of a package of interbedded clay and fine to very fine sand deposited in a transitional marine marsh and estaurine coastal environment, much like the area around the mouth of the Salinas River today. The sands commonly contain carbonized wood fragments and plant remains, along with shell fragments.

Sedimentology and microfossil studies of cuttings and sidewall cores from wells at Marina by Dr. James C. Ingle, Jr., of Stanford University confirms further details about the depositional environment of the deep aquifers in the Marina area. Also, based on foraminifera identification, no deposits older than uppermost Pleistocene have been penetrated by any of the Marina wells, including Well No. 12, which is 2,020 feet deep. Ash layers at a depth of 1,560 feet in this well may correlate with the "Olema Ash", which has been dated between 55,000 and 75,000 years BP.

The implication from the subsurface studies completed to date is that there is probably additional aquifer section of Pleistocene age at depth in the Marina "trough" than is presently being tapped by the existing wells.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California