Seen best in exposures on Kehoe Beach, the Laird Sandstone was likely a sandy, near shore or beach deposit, sometimes fossiliferous, that marks the return of the sea onto the Pt. Reyes Peninsula. There is are boulder conglomerate and abundant barnacle fragments in the basal member of the unit. Fossiliferous units are more well cemented and resistant to erosion.
Between the formation of the Pt. Reyes Conglomerate and the Laird Sandstone, Pt Reyes likely experienced a prolonged period of elevation and erosion. As the sea rose (or land sank) to create the Laird rocks, the environment quieted and the deposition of the Monterey Formation, which is also well exhibited in Kehoe Beach exposures, began and produced this great example of a transgressive sedmentary sequence.
Galloway's Laird Sandstone (Tl) descriptionMedium- to coarse-grained, commonly silty sandstone; friable; base commonly contains rounded to subangular granitic clasts from 2 to 24 inches in diameter; largely unbedded except where interbedded with siliceous shale near contact with Monterey Formation.Clark and Blake description:Laird Sandstone -- Very-thick-bedded, light-gray,medium-to-fine-grained, biotitic arkosic sandstone with scattered calcareous concretions locally includes a thick boulder granitic conglomerate at base. Rests nonconformably on the granodiorite and granite of Inverness Ridge and on the tonalite of Tomales Point. As much as 64 m thick at Kehoe Beach, this sandstone unit thins to the east to less than 12 m near Lairds Landing on Tomales Bay. Mollusks and
echinoids from near the base of the Kehoe Beach section are diagnostic of shallow-marine depths and middle Miocene age (Clark and others, 1991).