Once endemic to the San Francisco Bay Area --- specifically Alameda Creek, Coyote Creek, and Steamboat Slough --- the sooty crayfish was declared extinct in 2010. It probably disappeared earlier, as it was not sighted for the entirety of the twentieth century, vanishing from its native waters as the signal crayfish was introduced, a species that carry a water mold known as crayfish plague. Overharvesting and development of the Bay Area may have also contributed to its demise. It resembled the Shasta crayfish, but was smaller and blacker in color, rarely exceeding two inches (fifty-one millimeters) in size.