The bedrock strata dip moderately to the southwest of the reservoir. Minor, discontinuous faults locally cut the bedrock, but so not significantly disrupt the overall northwest tending synclinal structure. Throughout the site vicinity, alluvium, stream channel deposits, and artificial fill apron the hills and underlie the lower ground. Climatology Martinez has a climate typical of the coastal areas of southern and central California. Mean annual precipitation is about 18.00 inches, more than 95 percent of which fall during the cool season, from October to April.
Summers are nearly rainless.
Thunderstorms occur about two times per year based on records from San Francisco and Oakland. There is no preferred season for-thunderstorm occurrence. In the cool season, thunder is sometimes associated with convective activity imbedded in general rainstorms. In summer occasional intrusions of cold unstable air aloft or moist tropical air at low levels over California create conditions favorable for thunderstorm development.