The BLM site Westwater Canyon WSA
describing the Wilderness Study Area says it is on both sides of the river. In fact, it sounds like more territory will be on river left than on river right.
"This WSA spans the Westwater Canyon portion of the Colorado River with the eastern two-thirds located in the Dolores Triangle. Major tributary canyons on the east side of the river include Little Dolores, Marble, and Star canyons. A short box canyon, Little Hole, and a Rincon, Big Hole, are the main features northwest of the river."