The high bluff visible above South Beach, down the path about one quarter mile past the informational sign at the entrance to the beach, provides the most accessible views of three of the main geologic deposits in the Seattle area. From bottom (oldest) to top, they are the Olympia Beds, the Lawton Clay, and the advance outwash (also known as the Esperance Sand).

Lawton Clay is considered a ‘’type locality”- what geologists call the place where a deposit is first described and documented. It and the overlying advance outwash were both products of the last ice-sheet glaciation in the central part of the Puget Lowland, about 17,000 years ago. They rest on top of sediments deposited in an earlier, pre-glacial environment not unlike what we live in today.

The short bluff directly in front of the informational sign is composed of glacial till. It was deposited on top of the advance outwash. This Vashon Till formed directly beneath the ice sheet, and it is the ”hardpan” found at the ground surface across many of Seattle’s hills.

In October of 2024 an educational sign on the Geology of the South Beach Bluff was installed within view of the bluff. From trail marker 32 cross Discovery Park Boulevard towards the beach. The sign is visible right as you reach the beach. The sign made possible by the Friends of Discovery Park, with funding provided by the Neighborhood Matching Fund of the Seattle Dept. of Neighborhoods.

Photo of bluff by Marcus Donner, July 23, 2024.

Measured elevations adapted from Booth and Troost, 2008; adapted from Mullineaux et al., 1965.