Along these upper reaches, it flows roughly parallel to the highway, under which it passes several times before turning sharply north near the Horse Ridge Research Natural Area, 19 miles (31 km) southeast of Bend.

[5][6] Oregon Geographic Names says that the dry channel of the river, which runs in places between walls of basalt, is clearly marked for more than 50 miles (80 km), from the west end of the desert to the Crooked River.

[8] The canyon was carved during the wetter climate of the Pleistocene epoch by water flowing from a now-vanished lake in the Millican Valley.

[8][9] Canyon walls in this stretch rise 300 feet (91 m) above the sandy bed of the river.

[9] Other sights include large boulders, juniper trees, and Native American petroglyphs.