Angular unconformity in Utah, USA.

One of the world's most impressive angular unconformities is located along Interstate 70 in Salina Canyon, Sevier County, central Utah, USA.

Angular unconformities are formed by structural tilting of flat-lying sedimentary rocks, followed by erosion, followed by deposition of more flat-lying sedimentary rocks. The Salina Canyon angular unconformity can't get more angular than it is already. You've got flat-lying beds atop vertical beds, separated by an erosion surface having small-scale irregular topography.

This angular unconformity is exposed throughout the lower parts of Salina Canyon (Salina Creek valley), east of the town of Salina, on both sides of Interstate 70 (but better seen on the northern side of the highway). Eastward of the photo shown above (i.e., to the right of the viewer), the underlying rocks become less vertical, and eventually have a disconformable relationship with the overlying rocks. The structural tilting of the Twist Gulch in Salina Canyon has been attributed to local salt dome tectonics. Evaporites occur in the underlying Arapien Formation (Middle Jurassic). Some of the Arapien's rock salt intervals have domed upward as salt diapirs, resulting in tilting of overlying beds. The Salina Canyon angular unconformity provides information about the timing of Arapien rock salt diapirism (post-Jurassic & pre-Paleocene - in other words, during the Cretaceous).

The reddish-colored, vertically-oriented beds below the contact shown above are part of the Twist Gulch Formation (Middle Jurassic) - mainly siltstones, sandstones, and mudshales. The grayish-colored horizontal beds above the contact are sandstones of the basal Flagstaff Formation (mid-Paleocene).