bedrock

kallioperä, peruskallio

pohja, perusta puhekieltä The solid rock that exists at some depth below the ground surface. Bedrock is rock "in place", as opposed to material that has been transported from another location by weathering and erosion.
A basis or foundation.
2012 October 23, David Leonhardt, "http://www.nytimes.com/2012/10/24/us/politics/race-for-president-leaves-income-slump-in-shadows.html," New York Times (retrieved 24 October 2012):

Many of the bedrock assumptions of American culture — about work, progress, fairness and optimism — are being shaken as successive generations worry about the prospect of declining living standards.

Privacy is the bedrock of individual freedom.