This is called the Black Hill. The cut around it is a trail. Back when the Mormons were sent down to Southern Utah from the Salt Lake Valley by Brigham Young, the pioneers immediately set to building the St. George Temple. They cut rock from this hill for the base of the temple. The temple was being built in a swampy area. The people drained the land and then used the volcanic rock, which they crushed and laid down to create a dry good foundation for the building. The trail is called Temple Quarry Trail. Can you imagine cutting rock from this hill, and somehow getting it about 3 miles away to the temple site. They used 17,000 tons of volcanic rock and sandstone to build the temple.
The rock was hauled by wagons and mules.