Simplify the following text for a Grade 3 native English-speaking person.
Original: A U.S. post office was established on the site on June 15 , 1870 , and the name was changed to `` Grand Forks '' .
Simplified: Grand Forks is a city in the U.S. state of North Dakota along the Red River of the North . It was founded by Alexander Griggs on June 15 1870 .