Marias (mərĪˈəz) [key], river, c.210 mi (340 km) long, rising in several branches in NW Montana near the Continental Divide and flowing SE to the Missouri River near Fort Benton. It receives the Teton River. The Marias is used for irrigation. Tiber Dam (completed 1956), located in the lower course, is part of the Missouri River basin project.
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