I found fossils of shellfish in fragments of freshly fallen conglomerate on the trailside of Pacoima Creek, between Lopez Dam and the Lopez hills.

They are reminders, miles from today’s shoreline, that the San Fernando Valley was once embayed, the playground of scallops and clams. Later all that shallow bay muck was uplifted — crunched up — by convergence of the migrating West Transverse Range fault block against the edge of the North American craton. The line of suture where the fault block docked (at San Gabriel Fault) is now just a couple of miles north of this spot.