An early howler from the Register there - nicely spotted.
Mono Lake itself is actually the site of a number of active volcanoes; one of which on the lake's floor might have erupted as recently as the early 19th Century. It's the northern end of the Mono-Inyo craters chain which are also considered active and are intermittently seismically active.
Mammoth Mountain at the other end of the chain is as you say, another volcanic centre. It's a series of lava domes that came up more than 57,000 years ago. The mountain itself is not thought to be likely to imminently erupt, but again, there has been plenty of activity in and around the mountain. In the 1980s there was a lot of seismic activity around the mountain and increased CO2 flow from underground killed trees on the mountain which did put the USGS on alert.
All of these are associated with the colossal Long Valley Caldera which is the lesser-known sister of Yosemite. It's erupted a number of times in the Holocene, most recently about 60,000 years ago; but its biggest eruption was 760,000 years ago when it poured out an unbelievable 700km3 of white hot foam which fills a good part of the upper Owens Valley. That too is considered active with lots of seismic activity and regular ground deformation as magma slops around deep underground.
It is also a staggeringly beautiful area and well worth renting a car to visit if you're ever in California or Nevada.