1. Lewis and Clark Expedition: On July 19, 1805, Meriwether Lewis and William Clark arrived at the confluence of the Marias and Missouri Rivers in Montana. This area is now known as the Upper Missouri River Breaks National Monument.

2. Battle of the Rosebud: On July 19, 1876, a battle between the United States Army and Lakota Sioux, Northern Cheyenne, and Arapaho tribes took place in Montana. This battle was significant in the events leading up to the Battle of Little Bighorn.

3. The Anaconda Copper Mining Company: On July 19, 1921, the Anaconda Copper Mining Company acquired the assets of the Butte and Superior Mining Company. This acquisition made Anaconda one of the largest copper mining companies in the world at the time.

4. Big Hole National Battlefield: On July 19, 1990, the Big Hole National Battlefield was established in southwestern Montana. This area commemorates the Battle of Big Hole, which took place on August 9-10, 1877, between the United States Army and the Nez Perce tribe.

5. Earthquake: On July 19, 1959, a 7.5 magnitude earthquake struck near Hebgen Lake in southwestern Montana. This earthquake caused a massive landslide that killed 28 people and created a new lake, known as Earthquake Lake.