Mehrten Formation

The Mehrten Formation is a geologic formation in California that is a type of Inverted Relief that was principally formed of andesitic clastic and pyroclastic material that came from volcanos and filled rivers and valleys. Then that rock resist erosion better than the land around it leaving ridges that look like inverted rivers meanders.

It was originally described in the 1939 Geology and Ground-Water Hydrology of the Mokelumne Area, California, Piper et. al.

Naturalist John Muir described them as "dead rivers" in his writings. Also known as Inverted Relief.

It preserves fossils dating back to the Neogene period.