Complex sentence: In Oklahoma, the stream flows east across Beckham County where it joins Sweetwater Creek and then turns southeast to form the county line between Greer and Kiowa counties, where it is impounded to form Lake Altus-Lugert.
Split into simpler sentences: In Oklahoma, the stream flows east across Beckham County where it is joined by Sweetwater Creek. It then turns southeast to form the county line between Greer and Kiowa counties, where it is impounded to form Lake Altus-Lugert.