Bone Beds and Sand Dunes

Ocean Beach from Sutro Heights stretching south towards Montara Mountain in the distance.

These modest sand dunes are a remnant of a vast dune field that underlies much of San Francisco. Sand from Ocean Beach was blown up over the hills of San Francisco, forming dunes as far east as San Francisco's Financial District and the bay. The sand originated on a broad coastal plain that stretched 30 miles west, when the sea level was low during the last Ice Age.

The Colma Formation

As continental glaciers melted between about 18,000 and 5,000 years ago, sea level rose rapidly, and the coastal sand was transported inland. The underlying reddish Colma Formation, exposed in the bluffs below, was deposited during that Ice Age.

Mastadons by the Bay?

In 1886, near here, workers were digging a well for Adolph Sutro and found mastodon bones embedded in a clay bank of the Colma. As was typical of Sutro's interest in natural history, he put these relics on display at Sutro Heights.