Abert Rim is a steep cliff of many layers of hardened lava flows, extending 30 miles and rising 2,500 feet, formed as a fault scarp over millennia by great blocks of rock tilting and moving along faults in a region where the earth's crust is thinning and stretching. The fault that produced it is one of many in the Basin and Range Province, a geologic region where rising blocks of crust form mountain ranges and sinking blocks create broad basins across about 300,000 square miles, including almost all of Nevada and parts of Oregon, Idaho, Utah, California, Arizona, and New Mexico. Lake Abert, in the basin below, covers 63 square miles but is only a remnant of Ice Age Lake Chewaucan, which once covered over 470 square miles, and the older lake's shorelines still line Abert Rim's cliffs far above the present shorelines. Archaeological evidence shows that Native Americans have been here for about 11,000 years, with the greatest use between 2,000 and 500 years ago, and that most lived in earth covered lodge villages along Lake Abert's shoreline. Artifacts suggest these early people were affiliated with ancestors of the modern Klamath and Modoc Indians, who now live to the west.