Eastern Oregon is a region of the U.S. state of Oregon. It is not an officially recognized geographic entity; thus, the boundaries of the region vary according to context. It is sometimes understood to include only the eight easternmost counties in the state; in other contexts, it includes the entire area east of the Cascade Range. Cities in the basic eight-county definition include Baker City, Burns, Hermiston, Pendleton, Boardman, John Day, La Grande, and Ontario. Umatilla County is home to the largest population base in Eastern Oregon, accounting for 42% of the region's residents — more than twice that of the region’s second most populous, Malheur County. Hermiston, located in Umatilla County, is the largest city in the region, accounting for 10% of the population. Major industries include transportation/warehousing, timber, agriculture and tourism. The main transportation corridors are I-84, U.S. Route 395, U.S. Route 97, U.S. Route 26, U.S. Route 30, and U.S. Route 20.
Compared to that of the western part of the state, the climate of Eastern Oregon has a drier continental climate, with much greater seasonal variations in temperature. Unlike the Willamette Valley, Eastern Oregon receives a significant amount of snow in the winter. Some areas receive fewer than 10 inches (250 mm) of rain yearly, classifying them as deserts. This desert climate is in part due to a rain shadow effect caused by the Cascade Range. Pine and juniper forests cover 35% of Eastern Oregon, much in the mountains that include the Blue Mountains, Strawberry Mountains, Wallowa Mountains, Trout Creek Mountains, Ochoco Mountains, and Steens Mountain. Volcanic basalt flows from the Columbia River Basalt Group covered large sections of Eastern Oregon 6 to 17 million years ago. Other landforms include the Alvord Desert, Owyhee Desert, Warner Valley, Deschutes River, Owyhee River, Grande Ronde River, Joseph Canyon, The Honeycombs, and Malheur Butte.
