This formation is Dakota sandstone. There's a thin coat of sand covering the rocks which makes climbing on them a slippery experience. You also have to watch out for sticker plants and sharp yucca points. Much of The Rock was quarried in the late 1800s and used by the railroad and for buildings in town.
1972 was the 150th anniversary of the Santa Fe Trail. This plaque set into the formation honors William Becknell.
In 1976, a wagon train celebrating the country's bicentennial visited The Rock.
Preserving Pawnee Rock from was a joint effort in 1908. The Rock was at least twice the size before the quarrying.