White Canyon in San Juan County, Utah, has its origination in the foothills of the Abajo Mountains, runs through Natural Bridges National Monument, then runs alongside Scenic Byway 95 (ok, SB95 runs alongside White Canyon) until it crosses under SB95 just before it joins Glen Canyon and Lake Powell near Hite, Utah.
A look at the mapquest map tends to support the claim by American Southwest that SB95 actually winds through the wide canyon with the gorge alongside being what we usually call White Canyon:
The upper stretches are quite shallow but the gorge soon becomes wide and deep, bordered by crumbling red and white cliffs at either side - a scenic backdrop to UT 95, the Utah Centennial Highway, which winds through the canyon.
A narrow ravine cuts into the middle of the main valley floor, several hundred feet deep in places and although mostly quite open, some parts are more slot-like, especially the Black Hole, a permanently flooded section of 500 feet where the smooth grey/brown Cedar Mesa sandstone walls are just a few feet apart.
Wikipedia seems to agree when it says
Utah State Route 95 parallels the inner gorge of the canyon for much of its length.
White Canyon (as well as the White Rim in Canyonlands) gets its name from the bright white colored rock - Cedar Mesa Sandstone, Permian age. The red mesas/ridgelines of the surrounding upland (on both sides of SB95) consists of slope-forming Chinle Formation capped by cliffs of Wingate Sandstone, both of Triassic age. The entire Colorado Plateau with its varying rock structures is a geologic wonderland.
The photo gallery below has photos along the length of White Canyon, featuring the
black hole, the main attraction near the western end of White Canyon, with Natural Bridges National Monument being its attraction near its eastern end.
The photos are arranged from east to west.
Photos of SB95 are in the Scenic Byway 95 article, more photos of the natural bridges are in the Natural Bridges article.