Compression also caused low-angle thrust faults emplacing older rocks on top of younger ones. The largest of these thrust faults, the Alta Thrust, runs up the east side of Collins Gulch and has shoved the Tintic Quartzite atop much younger limestones.
| Much of the complex structural geologic history of Alta is visible in the Hellgate Cliffs. The grey and white bands are limestone and marble. Notice that these bands come to an abrupt halt near the left center of the photo. This is the location of a high angle normal fault which has juxtaposed the limestones with much older brown-weathering Tintic Quartzite. Above the black and white cliff, the brown-weathering Tintic Quartzite overlies the much younger limestones. This apparent inconsistency is the result of a low angle thrust fault that regionally pushed older rocks over younger ones. The pressure was from west to east. At the left edge of the photo dark bands in the Little Cottonwood Tillite define tight folding of the rock that probably occurred at the same time as the thrusting. |