Mountain Madness in Seattle also has a bunch of climbing programs as well as leading guided climbs both in the Pacific Northwest and internationally. I've done one of their schools--as well as taken a couple of their trips--although not recently.
They're all(?) dormant at this time but there are quite a few volcanoes on the West coast, the Cascades in particular, that could certainly become active. After all, it's only a few decades since Mount St. Helens exploded and the main blast area is still pretty, well, blasted.
Rainier is the iconic destination and the park is worth a visit. But it is crowded and there's a whole lot of wilderness and other summits throughout the Cascades.
Yes. The park’s many hydrothermal features attest to the heat still beneath this area. Earthquakes—1,000 to 3,000 per year—also reveal activity below ground. The University of Utah Seismograph Station tracks this activity closely."
Good reason to visit Seattle.