Even if you aren’t a professional geologist, the volcanic Panum Crater (Hwy. 120 three miles east of Hwy. 395, short dirt road to parking) is worth visiting. This rhyolite crater is only 600 years old—a mere baby in geologic time! Take a hike around the rim of the crater, and if you’re feeling up to it climb up the trail to the top of the plug dome.
Be sure to slather on the sunscreen since no trees shade these trails and it gets quite warm in the summertime. Check the Mono Lake website [1] for occasional guided tours of Panum Crater.
Links:
[1] http://www.monolake.org/