This complex is one of three probable sources of the volcanic clasts within the sandstone and conglomerate of the Miguelito and Edna members of the Pismo Formation in the Point Sur area 145–160 km (90-100 mi) to the north and west of the SG-SS-H fault.

Based on paleomagnetic signatures, the Morro Rock-Islay Hill Complex was rotated 40 to 50 degrees, perhaps during late Miocene or early Pliocene time.

Franciscan missionary and expedition member Juan Crespí noted in his diary that "we saw a great rock in the form of a round mountain (Spanish:morro)".

[14][15] The rock, which was quarried on and off from 1889 to 1969, provided material for the breakwater of Morro Bay and the improvements at Port San Luis Harbor.

[17] It presently serves as a reserve for peregrine falcons, which are locally endangered and cause most of the laws that prohibit intervention with avian life.

Other fauna include a wide selection of tide pool animals, like hermit crabs, small fish, starfish, sea cucumbers, mussels, bivalve mollusks, coral, and more.