Awesome find, Donny!
Looks solidly dated to the middle of the second Seminole war in Florida. July the 5th, 1839 was during this "cease fire" type of agreement. I copied this part of the Wiki story:
Macomb's peace and the Harney Massacre[edit]
In Washington and around the country in 1839, support for the war was eroding. The size of the Army had been increased because of the demands for manpower in the Florida war. Many people were beginning to think that the Seminole had earned a right to stay in Florida. The cost and time required to get all the Seminole out of Florida were looming larger. Congress appropriated US$5,000 to negotiate a settlement with the Seminole people in order to end the outlay of resources. President Martin Van Buren sent the Commanding General of the Army, Alexander Macomb, to negotiate a new treaty with the Seminole. Remembering the broken treaties and promises of the past, they were slow to respond to the new overtures. Finally, Sam Jones sent his chosen successor, Chitto Tustenuggee, to meet with Macomb. On May 19, 1839, Macomb announced reaching agreement with the Seminole. They would stop fighting in exchange for a reservation in southern Florida.[54]
As the summer passed, the agreement seemed to be holding. There were few killings. A trading post was established on the north shore of the Caloosahatchee River, and the Seminole who came to the trading post seemed to be friendly. A detachment of 23 soldiers was stationed at the Calooshatchee trading post under the command of Colonel William S. Harney. On July 23, 1839 some 150 Indians attacked the trading post and guard. Some of the soldiers, including Colonel Harney, were able to reach the river and find boats to escape in, but most of the soldiers, as well as a number of civilians in the trading post, were killed. The war was on again.[55]
