Coulees

Coulees are broad, steep-sided valleys or drainage corridors, typically formed by erosion and often characterized by dry or seasonal stream beds. The term is chiefly used in North America, particularly in the western United States and the Canadian prairies.

Etymology and usage: The word comes from the French coulee, a feminine past participle of couler, meaning to flow. In English, it describes channels and valleys carved into plains and plateaus by flowing water or by lava, often implying a wide, flat-bottomed valley with high sides.

Formation: Coulees commonly form where thick lava flows created a flat, resistant surface that was later eroded by streams to produce deep, broad valleys. They also develop where rivers carve through soft sediments or through glacially sculpted terrain, creating broad benches and vertical or near-vertical walls. Many coulees are dry or have intermittent water flow for parts of the year.

Geographic distribution: The term is widely used in the Columbia Basin and the Pacific Northwest, and across the Canadian Prairies. Notable examples include the Grand Coulee in Washington, a large canyon carved by the Columbia River through flood-basalt terrain; numerous other coulees stretch along tributaries in Alberta, Saskatchewan, and Montana.

Ecology and land use: Coulees host mosaic vegetation adapted to dry upland conditions and support wildlife such as deer and various bird species. They are often used for grazing, and where water is available, for irrigation and farming along their edges. Some coulees are popular for recreation, offering viewpoints, trails, and access to escarpments.