Summer Lake (Oregon) - Ancient Lake Chewaucan

Ancient Lake Chewaucan

The arid lands around Summer Lake were once lush. During the Pleistocene Epoch, vast areas of this region of south central Oregon were covered by lakes and wetlands. As the last ice age was ending, rain and runoff from melting snow filled the lowlands throughout this region of the Great Basin, creating an immense, freshwater lake called Lake Chewaucan. The lake covered 461 square miles (1,190 km2) at depths of up to 375 feet (114 m).

Lake Chewaucan covered the Summer Lake basin and drainage system much of the late Pleistocene. The last high water period is thought to have occurred about 13,000 years ago. There is no archaeological evidence of human utilization of Lake Chewaucan during this time. The earliest evidence for possible human occupation of the basin comes from the Paisley Caves excavated by Luther Cressman in the late 1930s. Cressman found some inconclusive evidence that humans could have begun occupation of the Summer Lake area around 11,000 years ago.

Lake Chewaucan began to dry up at the close of the Pleistocene. As it shrank, salts and alkali were concentrated in its remaining waters. The exposed lake bottom sediments were blown by the prevailing westerly winds to form the sand dunes that still lie on the east side Summer Lake.

Today, Summer Lake and Abert Lake are separated by 20 miles (32 km) and are the only remnants of Lake Chewaucan. At high water, Summer Lake is about 15 miles (24 km) long and 5 miles (8 km) wide; however, water levels fluctuate dramatically, and sometimes the lake is almost dry in summer. The main source of fresh water is the small spring-fed Ana River, which is used for irrigation.