http://en.wikipedia.org/wiki/Sooners
The term Sooners was used to describe settlers who entered the Unassigned Lands, located in the current state of Oklahoma, before President Grover Cleveland officially proclaimed them open to settlement with the Indian Appropriations Act of 1889 on March 2, 1889. The name derived from the "sooner clause" of the Indian Appropriation Act, which stated that no one should be allowed to enter and occupy the land prior to the opening time and that such people would be denied rights to illegally claimed land.[1]
Sooners were often deputy marshals, land surveyors, railroad employees, and others who were able to legally enter the territory early.[2] Some sooners crossed into the territory illegally at night and were originally called "moonshiners" because they entered "by the light of the moon." These sooners would hide in ditches at night and suddenly appear to stake their claim after the land run started, hours ahead of legal settlers.[1]