Monitor and Merrimac refer to what in the passage?

Merrimac Butte[2] is a 5,627-foot (1,715-metre) sandstone summit located in Grand County, Utah, United States, about 12 miles northwest of the town of Moab. Merrimac Butte is a thin, 200–600-foot-wide and 1,600-foot-long east-to-west butte with 200-foot-tall vertical Entrada Sandstone walls overlaying a Carmel Formation base.

Monitor Butte is situated immediately east of Merrimac Butte. The two buttes were named after the Monitor and Merrimack, two ironclad steamships known for clashing during the American Civil War. They can be seen from Highway 313 after it climbs out of Sevenmile Canyon en route to the Island in the Sky section of Canyonlands National Park or Dead Horse Point State Park.

Monitor and Merrimac are two buttes which sit next to one another in Utah, U.S. These names are taken from two ironclad streamships of the American Civil War.