Isocapnia mogila, a rare winter stonefly, is found in good numbers in Humboldt County, California. In the 50 years since this species was described, very few specimens were recorded from only 4 sites in California and Oregon. Emergence seems to be higher in the fall and early winter than in the late winter and spring.
Baumann, Richard W. and Lee, Jonathan J.
"Discovery of a large population of the rare winter stonefly Isocapnia mogila Ricker in the Mad River, California (Plecoptera, Capniidae),"
Western North American Naturalist: Vol. 67
, Article 15.
Available at: http://scholarsarchive.byu.edu/wnan/vol67/iss4/15