The Sacramento Valley, which forms most of the northern one-third of the Central Valley, is a broad structural trough. The study area comprises the valley floor and some of the foothills of the Sierra Nevada and the Coast Ranges, a total area of about 6,000 square miles.
Beneath most places in the valley, the base of the post-Eocene continental deposits is equivalent to the base of the Tehama Formation of Pliocene age, which in some places at least may be of late Oligocene and early Miocene age. The deposits consist of intercalated beds of gravel, sand, silt, clay, tuff, conglomerate, sandstone, siltstone, and claystone. And beneath large areas along the eastern side of the valley the deposits consist of basaltic and andesitic mudflows, tuff, tuff breccias, volcanic sandstones and conglomerates, and sand and gravel, as well as overlying nonvolcanic sediments. They contain most of the fresh ground water in the valley.
The structure of the base of the continental deposits is that of a large northward-trending syncline whose trend is interrupted only by the Sutter Buttes. In the subsurface, faulting has occurred mostly within the basal part of the deposits. Beneath the northeastern part of the valley, along the Chico monocline, faulting has occurred through probably the total thickness of the deposits.
The deposits range in thickness from zero near the margins of the valley to about 3,500 feet beneath the south-central part of the valley. The thickest sections occur along the axis of the syncline, but near Sutter Buttes the deposits are thinner than at any other locale near the central part of the valley.
|Title||Base and thickness of the Post-Eocene continental deposits in the Sacramento Valley, California|
|Authors||R. W. Page|
|Publication Subtype||USGS Numbered Series|
|Series Title||Water-Resources Investigations Report|
|Record Source||USGS Publications Warehouse|