[1] The formation rocks comprise the barrier bar[1] for Los Peñasquitos Lagoon[2] and have three sub-facies that can be classified as ancient oyster reefs (Ostrea idrianensis), tidal flats and sublittoral channels and ponds[1] The formation is a result of sedimentary infilling of a large Eocene Delmar lagoon[3] and contains fossils from that period.

[5] Delmar Formation consists of dark green claystone and mudstone, greenish-gray muddy sandstone, interbeds formed by biostromes of shells of molluscs.

[6] The Delmar formation can be observed, together with Torrey Sandstone, for 20 kilometers along the seashore, from Encinitas to the Torrey Pines State Park, both extend up to 13 kilometers inland, and are expected to go to farther in the subsurface in the southwestern direction.

)[8] and macrofossils (mollusc shells),[9] with the latter indicating the brackish water conditions.

[10] Plant material can be also found in the form of remains of grass blades and wood fragments.