Giant Garter Snake Posted on August 18, 2018 by Mike Pingleton Leave a comment Thamnophis gigas Fitch, 1940 Colusa Co., California. May 8, 2014. Opaque, battered and bloodied, this large female was found on the banks of an irrigation ditch. This species is featured in my Notes From The Field blog post ‘Thamnopalooza‘. My Flickr album for this species is here.