The geology of Eagle Lake is unique. It is a mixture of Sierra Nevada spillover (Gallatin Peak) and the Cascades that flanked Gallatin on both sides. One can see transition from the tailing pile remnants of Bly Tunnel. The inlet consisted of decomposed granite (Sierra) while the outlet tailings is red volcanic cinder (Cascade).
In 2017 U.S.G.S. released Age of the Youngest Volcanism at Eagle Lake, Northeastern California. It is only a 34 page document which I can hopefully one can access it this way. If not please email and I will send you the pdf file.
Clynne etal USGS OFR 2017-1027 Eagle Lake
Tim
No speak the language but somehow knew Susanville/Eagle Lake was the transition zone.