Skip to main content.


15. Pluvial Lakes: Oregon’s inland seas

Exotic Terranes

Over the past 2 million years, climate change caused ice ages to occur again and again. During these times, increased rainfall filled many of the large closed basins in eastern Oregon, forming big bodies of water called pluvial lakes. Lakes as large as 500 to 1000 square miles filled the Harney, Klamath, Catlow, and Goose Lake basins as well as innumerable other smaller basins. Most eastern Oregon lakes, like Summer Lake, Hart Lake, and Lake Abert, are lonely salty remnants of great pluvial lakes, whose ghostly shorelines can be seen high above the modern shores. When the next ice age occurs, these ancient lakes will fill again.

OGDC units: Quaternary playa lake deposits, and Quaternary alluvium, pluvial lake deposits and terrace deposits in closed basins

Age Range: 2 million to 10,000 years ago
Rock Types: gravel, sand, silt, clay
Did You Know? Fort Rock Lake was the largest pluvial lake in Oregon. It covered over 1260 square miles to a depth of 320 feet in Fort Rock and Christmas Valleys.
square bullet Go See It!
Fort Rock State Natural Area
Lake Abert
Hart Lake


« Back    Continue »