Geology of Torrey Pines State Natural Reserve

This Geology section, including all the following pages, was written by Don Grine, Geophysicist Emeritus*

A geology walk with GPS coordinates

The Big Picture: Time, Plates, and Sea level

Painting of Broken Hill
& flowers by J. J. Grine

Although the rocks in Torrey Pines State Natural Reserve are partially obscured by the trees and wildflowers, you can see some interesting geology. The rocks are always in full bloom. You should be particularly interested because we live inside the fault zone between the Pacific plate and the North American plate.

Geologic time is long beyond human experience. We can give an example from the measured movement of the mostly rigid thin plates that move over the surface of the Earth like bits of eggshell over an egg. Torrey Pines Reserve is near the edge of the Pacific plate, moving toward the Aleutians at about two inches per year. If the movement continues, we will be dragged under the Aleutian chain in about eighty million years and spewed up as molten rock. We have some faults on our ocean side so we may get left behind a bit as a small island.Most of the rocks in the Reserve were deposited in or near the ocean. Sea level has changed relative to the land. During the last ice age, about 20,000 years ago, sea level was 300 feet lower than now. The lagoon to our north was carved 300 feet deeper than its present mud floor, then filled with mud when the ice melted and the sea rose. If global warming melts all the ice in Antarctica and Greenland, sea level will be 300 feet higher, lapping at the Lodge.

Next topic: Rock formations