https://en.m.wikipedia.org/wiki/Great_Valley_Sequence
The Great Valley Sequence contains several geologic formations. Because geologists studying this sequence in different areas have used different formation names over the years to describe the same packages of rocks, the nomenclature is complex and confusing. Parts of the sequence are well exposed at several places along a line of outcrops that extends for about 150 miles (241 km) along the west side of the Sacramento and San Joaquin valleys (both of which make up the Great Valley of California). These same rocks are also found in several deep wells in oil and gas fields located in the center of the valley. Geologists working these different areas independent of each other developed different sets of formation names for the different areas. Yet refinements in dating the ages of the different units has led to the realization that an interval of rock in one area may be exactly the same age as the rocks in another area, yet be referred to by a completely different formation name.[10]
Some of the best outcrops for these rocks are on the west side of the southern Sacramento Valley at Putah Creek and Cache Creek canyons. The formation names used here extend to the subsurface where several gas wells in the center of the valley produce from the same rocks, and from younger rocks that overlie them. Although the younger rocks are not exposed in the canyons to the west, most geologists combine the formation names from the west side outcrops with the subsurface names from the gas fields to create a coherent set of names that is largely agreed upon for most of the Sacramento Valley.[11]
The same is not true for the San Joaquin Valley to the south, where another area of well-known outcrops is found in the hills to the west of Coalinga. This area uses a completely different set of formation names for exactly the same group of rocks as are found to the north. Yet another set of formation names is applied to Great Valley rocks penetrated by oil and gas wells in the subsurface northeast of Coalinga in the area near Stockton in the northern part of San Joaquin Valley. In addition, there are several lesser known areas in the San Joaquin Valley that each have their own terminologies. All of these names are firmly established in the geologic literature and attempts to set up a unified set of formation names have not met with success. An exception are the Jurassic-age rocks of the Great Valley Sequence, which most geologists assign to the Knoxville Formation, irrespective of location.[12]
Rock? Vault line depths?