- a mass of anhydrite, gypsum, or limestone immediately above the salt of a salt dome.
- an impervious stratum overlying an oil- or gas-bearing structure.
Origin of cap rock
An Americanism dating back to 1865–70
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for cap rock
Let's light out for the cap-rock an' hole up for a coupla days.
By the time Wadley reached the rough country of the cap-rock, the young day was beginning to awaken.
But when he saw yore son strike straight across country to the cap-rock, he trailed him to see where he was goin'.
Overstreet could do as he pleased, but he intended to slap a saddle on his horse and make tracks for the cap-rock country.
The discussion renewed itself as soon as the outlaws had hidden themselves in a pocket of the cap-rock.
- a layer of rock that overlies a salt dome and consists of limestone, gypsum, etc
- a layer of relatively impervious rock overlying an oil- or gas-bearing rock
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012