The Grande Ronde Valley is a valley in Union County in northeastern Oregon, United States. It is surrounded by the Blue Mountains, and is drained by the Grande Ronde River. La Grande is its largest community. The valley is 35 miles (56 km) long, north to south, from Pumpkin Ridge to Pyles Canyon, and 15 miles (24 km) wide, east to west, from Cove to the Grande Ronde River's canyon. Its name, fittingly, means "great circle".