Yahi is an extinct language

Extinct language

An extinct language is a language that no longer has any speakers., or that is no longer in current use. Extinct languages are sometimes contrasted with dead languages, which are still known and used in special contexts in written form, but not as ordinary spoken languages for everyday communication...

 formerly spoken in the upper Sacramento Valley

Sacramento Valley

The Sacramento Valley is the portion of the California Central Valley that lies to the north of the San Joaquin-Sacramento Delta in the U.S. state of California. It encompasses all or parts of ten counties.-Geography:...

 area, roughly in the area between Mill Creek

Mill Creek, California

Mill Creek is a small town in Tehama County, California most noted for its close location to Mount Lassen. It is located at an elevation of 4737 feet ....

 and Deer Creek

Deer Creek (California)

Deer Creek is a large stream in Northern California that flows through Tehama County, California. It is an eastside tributary of the Sacramento River, draining . The creek flows roughly southwest for most of its length. Its headwaters are in Lassen National Forest at an elevation of on Butt...

. It is grouped with the Southern forms of the Yana language

Yana language

Yana is an extinct language isolate formerly spoken in north-central California between the Feather and Pit rivers in what is now Shasta and Tehama counties....

s which, together with Central and Northern Yana are an isolated group

Language isolate

A language isolate, in the absolute sense, is a natural language with no demonstrable genealogical relationship with other languages; that is, one that has not been demonstrated to descend from an ancestor common with any other language. They are in effect language families consisting of a single...

 of languages. Yana is well known as having been the language of Ishi

Ishi

Ishi was the last member of the Yahi, the last surviving group of the Yana people of the U.S. state of California. Ishi is believed to have been the last Native American in Northern California to have lived most of his life completely outside the European American culture...

, the last surviving Yana Indian

Yana people

The Yana people were a group of Native Americans indigenous to Northern California in the central Sierra Nevada Mountains, on the western side of the range. The Yana-speaking people comprised four groups: the Northern Yana, the Central Yana, the Southern Yana, and the Yahi...

, who worked with anthropologists to make a record of the language and culture.