Park officials say a visitor spotted 26-year-old Dakota D. Tipton of Joshua, Texas, scratching the initials "DDT" into the keystone above a small walkway arch on one side of the larger arch on June 10.
Tipton appeared via phone for sentencing today by US Magistrate Judge Mark Carman in Mammoth Hot Springs, Wyoming.
The US Marshal's Service will determine where Tipton will serve his sentence.
The inscription on top reads: "For the benefit and enjoyment of the people.