It struck at 12:05 am local time at a depth of 11.4 kilometers. The USGS reports that the epicenter was 24 miles (39km) east-southeast of Missoula, 29 miles (47 km) south of Seeley Lake, 45 miles (74km) northeast of Hamilton and 70 miles (114 km) west of Helena.
Other small earthquakes have hit Montana recently and Kaj18.com reports that on December 30 a small magnitude 3.5 earthquake struck 14 miles away from Clinton. Prior to that a magnitude 3.3 earthquake hit near to Clinton in November. There are already reports on the USGS site from some people who felt the quake. - Only Kent.
Montana sits atop the Yellowstone Caldera, located in the Yellowstone National Park. The Caldera is the largest supervolcano on the American continent and considered as being active.
It has erupted with tremendous force several times in the last two million years. Half of the world's geothermal features are in Yellowstone, fueled by this ongoing volcanism. Lava flows and rocks from volcanic eruptions cover most of the land area of Yellowstone. The park is the centerpiece of the Greater Yellowstone Ecosystem, the largest remaining, nearly intact ecosystem in the Earth's northern temperate zone. - Wikipedia.