The arid land around Lake Abert was once lush. During the Pleistocene epoch, vast areas 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 Abert and Summer Lake basins for most of the late Pleistocene epoch. The last high water period occurred about 13,000 years ago.
Lake Chewaucan began to dry up at the close of the Pleistocene epoch. As it shrank, salts and alkali were concentrated in its remaining waters, and the result was the formation of Lake Abert and Summer Lake. Today, the two lakes are 20 miles (32 km) apart and are the only remnants of Lake Chewaucan.
Lake Abert is an endorheic body of water that occupies the eastern arm of pluvial Lake Chewaucan basin. The lake has an elongated triangular shape. It is approximately 15 miles (24 km) long and 1 mile (1.6 km) wide at the south end of the lake, growing to 7 miles (11 km) wide at the north end. In total, the lake covers approximately 57 square miles (150 km2). Despite its size, the lake’s maximum depth is only 11 feet (3.4 m). Its average depth is 7 feet (2.1 m).
The east side of Lake Abert is bounded by Abert Rim (see the related earthcache) , a steep escarpment that rises over 2,500 feet (760 m) above the lake surface. The lake is bordered on the west by a long ridge called Coligan Buttes and on the north by the Coleman Hills. The lake’s only year-around source of fresh water comes from the Chewaucan River, which flows into the lake from the south.
The Lake Abert drainages area covers 820 square miles (2,100 km2). The environment in the Abert drainage basin is semi-arid. Most of the precipitation in the area occurs as snowfall during the winter months, and the Chewaucan River system is fed primarily by seasonal snowmelt. The lake’s only other source of fresh water are summer thundershowers that produce a small amount of runoff from Abert Rim. Because the lake has no outlet, it has developed a high concentrations of sodium carbonates, common salt, and alkali in its water. Crystallized mineral crusts on rocks along the lakeshore can be several inches thick. Some mineral deposits are evident on boulders 300 feet (91 m) above the present lake surface.
To log this cache, please email the cache owner with an estimate of the distance from the road shoulder to the water (both the change in elevation and the linear distance. Do you see any mineral deposits where the water has receded? What color are they? Based on the deposits, what would you say about the changes in water level here?