1. The Helena earthquake: On March 15, 1934, a 6.3 magnitude earthquake struck the city of Helena, Montana. The earthquake caused significant damage to buildings and infrastructure, including the Montana State Capitol building.

2. Creation of Yellowstone National Park: On March 15, 1872, President Ulysses S. Grant signed a bill into law that created Yellowstone National Park in Montana, along with parts of Wyoming and Idaho. This was the first national park in the United States.

3. Montana becomes a state: On March 15, 1889, President Benjamin Harrison signed a bill that granted statehood to Montana. At the time, Montana was the 41st state in the union.

4. The Battle of Thompson Falls: On March 15, 1885, a skirmish broke out between the United States Army and Native American tribes in Thompson Falls, Montana. The battle was a part of the ongoing conflict between settlers and indigenous peoples in the American West.

5. The Granite Mountain mine disaster: On March 15, 1917, a tragic mining accident occurred in the Granite Mountain mine near Butte, Montana. A fire broke out in the mine, trapping and killing 168 miners. This was one of the worst mining disasters in U.S. history.