Sandstones interbedded with the shales are arkosic, light gray to tan, and sometimes massive, as at the base of the type section on Hollister Ranch.

[2][5] Another interbedded unit occasionally encountered is a cobbly conglomerate, which outcrops on the north slope of the Santa Ynez Mountains south of Gibraltar Reservoir.

[2][4] The region of present-day Santa Barbara and Ventura County during the Late Cretaceous was submerged, and the depositional environment was one of a narrow shelf and submarine fans.

Periodic episodes of deeper and shallower water resulted in finer and coarser sediments, respectively – shales versus sandstones.

[7] The crustal block on which the Jalama formation was deposited has been inferred to have rotated approximately 90 degrees clockwise and moved northward along the coast from its former position nearer San Diego.