caprock

• cap rock

From cap +‎ rock.

caprock (countable and uncountable, plural caprocks)

1. (geology) A harder or more resistant rock type overlying a weaker or less resistant rock type.
   • 2009 September 3, James Glanz, “Energy Company Calls Halt to Drilling Project”, in The New York Times‎^[1], archived from the original on 11 February 2021:

     Last month, federal scientists said that the company had fallen far behind schedule because a huge rig hired to drill down about 12,000 feet, or more than two miles, on federal land had not been able to pierce surface formations called caprock.

   • 2013, Philipp Meyer, The Son, Simon & Schuster, published 2014, page 424:

     Meanwhile, there were houses going up within gunshot of the caprock.

   • 2018 July 17, Autumn Spanne, “Check out these crazy rock formations across the United States”, in CNN‎^[2]:

     This park’s strange and beautiful rock formations were formed by the Yellowstone River and various streams that have cut through the rock over millions of years, carving out hoodoos, spires and caprocks. The name Makoshika comes from a Lakota word for badlands.