There is mention of Mono and lil' Eden in the2019 edition of "Hotsprings abnd Pools of the Southwest." There is the resort, Mono. There is mentioned some springs and old resort ruins tubs across the river. Across the river, swim suits recommended in the "daytime."
Little Eden is listed as clothing optional. The water pops out from below at 100F, but it is only around 90F.
Jbee