A "rock arch" refers to a natural formation of rocks that creates an arch shape. It is like a doorway made out of rocks created by erosion over a long period of time. Full definition
If you haven't guessed it by now, the Tianmen Road ascent is the latest challenge completed by the Range Rover Sport after the PHEV model climbed the 999 steps to the Heaven's Gate natural rock arch at the road's summit last month. (drivemag.com)
The most dynamic aspect of the economy is tourism, with a number of natural resources which are apt for this purpose, such as the grey whales that come to the area to breed and the natural rock arch at Land's End is frequently photographed. (en.wikipedia.org)