The Tulare Formation


The Tulare Formation is a largely non-marine, Pleistocene-age geologic unit in the San Joaquin Valley that represents the last episode of tectonic upheaval (mountain building) to take place in the valley. It represents what geologists at one time referred to as "molasse deposits". Thus, the Tulare is folded and deformed on the basin margins, where it is unconformably overlain by flat-lying, undeformed Recent alluvium. The angular unconformity at the top of the Tulare becomes conformable towards the basin center, where the formation is nearly impossible to distinguish from Recent alluvium above it, if age diagnostic fossils are absent. Although the Tulare in many places is composed of fluvial conglomerates, such as those shown in the photo on the right, it is an incredibly diverse formation, as is evident in the sampling of photos collected here, and it ranges from alluvial and lacustrine to nearshore and brackish-water environments. The Tulare overlies marine sediments of the San Joaquin Formation.

(The photo on the right shows fluvial conglomerates in the Tulare Fm on the Spellacy Lease at Midway-Sunset Field.)


A Gallery of Pictures from the Tulare Formation

Faulted Tulare Fm redbeds at Midway-Sunset Field.

A core of the Tulare Fm with the trace fossil of a tree root, and insect burrows at the base of the root (white light left & UV light right).

Two different Tulare cores: the left core contains non-marine insect burrows, and the right one contains marine bivalves.

Tulare Fm fluival redbeds overlying gray-green lacustrine shales at North Midway Field.

Sulphur-rich, yellow gypsum from lacustrine deposits in the Tulare Fm that are mined at the Holway Gypsum Mine near Lost Hills.

Tulare Fm channels cropping out of a hillside. The channels are lens-shaped, crossbedded sandstones imbedded in a shale matrix. A close-up of a channel is shown on the right.

A close-up of one of the crossbedded, Tulare Fm channel sandstones shown on the left. This photo and the one to the left are from North Midway Field.