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.

The Columbia River Plateau was created by a series of basalt flood eruptions.

Communities within the valley include Cove, Imbler, Island City, La Grande, Summerville, and Union.

The Grande Ronde River flows through the valley; its tributaries include Catherine, Fir, Ladd, Little, Mill, Pyles, and Willow creeks.

[9] The first permanent settler in the Grande Ronde Valley was Benjamin Brown, an Englishman who had originally settled in Michigan.

[10][11] Early settlements were in the more arable northern parts of the valley, as the southern end was subject to flooding, swampy, and contained alkaline soil.

This settlement grew into the city of Union, the second largest community in the Grande Ronde Valley.

[7] Mormons followed and settled in the valley after then, and remained a prominent force until the Nibley-Stoddard mills were purchased or closed between 1920 and 1931.

[7] The influence of the Mormons in the area was limited, as all profits were sent to Utah, rather than staying with local businessmen.

As one pioneer woman in the area wrote, "No more big, heavily loaded freight wagons with their wheels buried to the hub in mud.

[15] The Oregon Railway and Navigation Company (OR&N) built a spur line from La Grande to Elgin.