A signal crayfish (Pacifastacus leniusculus). Sadly a species that shouldn't be present in the waterways of central California - but has permeated the waterways here. It can now be found thriving well outside its native range which just barely dips into the northernmost reaches of California & is centered in Washington & Oregon. Even more sadly is that historically this stream may have been occupied by sooty crayfish (Pacifastacus nigrescens), a crayfish not dissimilar to this that quickly went extinct following the introduction of signal crayfish (this species) in the 1900s, searches in 1959,1977,1980,1981 all failed to turn up the native species - unfortunately, California's only other endemic native crayfish (shasta crayfish) is also endangered in part because of this species intrusion into its range.