La Honda Basin Oil Fields
S. T. Hector
Gotland Oil, Inc., Bakersfield, CA
La Honda Basin is one of the oldest, least productive of California’s oil basins. This onshore basin covers much of San Francisco Peninsula and contains oil fields a few miles south of San Francisco. Production found at Half Moon Bay and Moody Gulch in the late 1800’s was likely spurred by the presence of oil seeps. Subsequent exploration resulted in discovery of four fields— Half Moon Bay (1890), La Honda (1956), Oil Creek (1955) and Moody Gulch (1878)—with less than 2 million barrels of oil recovered.
The largest field by far is La Honda, which contains two oil accumulations on the adjacent and parallel La Honda and Haskins Hill anticlines. The Main Area, on La Honda anticline, is a buried domal trap, which produces high-gravity oil from the Eocene Butano sandstone. The Butano also produces light oil on the Haskins Hill fold, in an area known as the South Area. However, most oil at South Area comes from an unconformity trap of the Miocene Burns Limestone. In addition, a small amount of oil is trapped beneath the Pliocene unconformity in the Vaqueros sandstone.
Other fields with anticlinal traps include Oil Creek, where a faulted anticline contains oil in Eocene sandstones, and Half Moon Bay, where anticlinal traps house oil and gas in Pliocene sands.Moody Gulch, which produced high-gravity oil from very shallow depths, appears to be a large “seep” in faults associated with the San Andreas fault. This field was abandoned in 1960 to make way for State Highway 17.
La Honda Basin is structurally complex. Sandwiched in between the Hosgri-San Gregorio fault system and San Andreas fault, this basin has been uplifted, faulted, folded and eroded several times. Erosion has breached many large folds, severely limiting the possibilities of large finds in the basin. Nonetheless, this basin maintains oil and gas potential in small pools that may still exist adjacent to existing fields.
AAPG Search and Discovery Article #90904©2001 AAPG Pacific Section Meeting, Universal City, California