15 JUL--This Day in US Military History

1806 – Zebulon Pike, the U.S. Army officer who in 1805 led an exploring party in search of the source of the Mississippi River, sets off with a new expedition to explore the American Southwest.

Pike was instructed to seek out headwaters of the Arkansas and Red rivers and to investigate Spanish settlements in New Mexico. Pike and his men left Missouri and traveled through the present-day states of Kansas and Nebraska before reaching Colorado, where he spotted the famous mountain later named in his honor. From there, they traveled down to New Mexico, where they were stopped by Spanish officials and charged with illegal entry into Spanish-held territory. His party was escorted to Santa Fe, then down to Chihuahua, back up through Texas, and finally to the border of the Louisiana Territory, where they were released.
Soon after returning to the east, Pike was implicated in a plot with former Vice President Aaron Burr to seize territory in the Southwest for mysterious ends. However, after an investigation, Secretary of State James Madison fully exonerated him. The information he provided about the U.S. territory in Kansas and Colorado was a great impetus for future U.S. settlement, and his reports about the weakness of Spanish authority in the Southwest stirred talk of future U.S. annexation.
Pike later served as a brigadier general during the War of 1812, and in April 1813 he was killed by a British gunpowder bomb after leading a successful attack on York, Canada.

https://thisdayinusmilhist.wordpress.com/2005/07/15/july-15/