Manzanar National Historic Site Geology: An Alluvial Fan Below the Rising Sierra Nevada

The Manzanar Geologic Resources Inventory report. National Park Service.

Manzanar National Historic Site lies against the backdrop of the Sierra Nevada in Inyo County, California, on the western side of the Owens Valley — on an alluvial fan sloping east, about 8 km (5 mi) east of the Sierra Nevada Front escarpment.

• Authorized as a Park Service unit on March 3, 1992, it protects 329 hectares (814 acres) of natural, cultural and historical resources, including those tied to the relocation and incarceration of about 120,000 Japanese Americans during World War II.
• Besides its long history of human settlement, it records a rich geologic history, with active tectonics still reshaping the land.

The ground at Manzanar

Most of the area's geologic story is hidden: the site sits on Quaternary valley fill and has no bedrock outcrops. Its surface is almost all Holocene alluvium, with a small patch of older Pleistocene alluvium at its western edge.

A valley still being made

The last few million years in the Owens Valley have brought faulting, volcanism, glacial deposits and large lakes.

• The valley's major transform-normal faults are still active. Basin and Range–style crustal extension keeps lifting the mountains relative to the valley floor.
• Working against that uplift, glaciers, wind and water wear down the highlands and pour immense amounts of sediment into the valley.

Manzanar belongs to the Cascade-Sierra Mountains Physiographic Province and shares its geologic history with a region far beyond the site.

The site's geologic map. National Park Service, Geologic Resources Inventory.

Maps and reports

The NPS Geologic Resources Inventory makes digital geologic maps, reports, posters and scoping summaries for more than 270 natural resource parks; Manzanar's are in the NPS DataStore, with its completed Soil Resources Inventory. The NPS Geodiversity Atlas draws these together for education, geoconservation and park management.

Sources

Based on "NPS Geodiversity Atlas—Manzanar National Historic Site, California," National Park Service, citing Thornberry-Ehrlich (2009), Tweet and others (2016) and Anderson (2017); a work of the United States government in the public domain. Its cross-section of the Owens Valley, a Colorado State University graphic, is not reproduced.