Yes, it's local stone, called marlstone – basically a limestone that has iron in it, I think, hence the lovely rusty colour.    From Wordnik.com.  [Ginger Bread, Ginger Beer] Reference

To extract the kerogen, you crush and heat the marlstone.    From Wordnik.com.  [High Country News - Most Recent] Reference

The leftover marlstone takes up about 30 percent more volume.    From Wordnik.com.  [Aspen Times - Top Stories] Reference

This is clearly a place that could use fill - crushed marlstone by the cubic mile.    From Wordnik.com.  [Aspen Times - Top Stories] Reference

Granted, some of this energy would be need to haul the marlstone up to the Great Divide before starting down.    From Wordnik.com.  [Aspen Times - Top Stories] Reference

On the left is a ruined castle, built of shelly marlstone, which, according to Arabian tradition, once belonged to the Berdovil in question.    From Wordnik.com.  [The Caravan Route between Egypt and Syria] Reference

Belemnites are generally found in immense numbers together, especially in the marlstone quarries of the Midlands, and in the lias cliffs of Dorsetshire.    From Wordnik.com.  [Falling in Love With Other Essays on More Exact Branches of Science] Reference

Harish lies along the side of an undulating hill fronting the sea, at the foot of the large quadrangular castle, a substantial building of calcareous marlstone.    From Wordnik.com.  [The Caravan Route between Egypt and Syria] Reference

When there is an upper story, which is rarely the case, it is approached from the courtyard by a staircase, usually dilapidated, with stairs of shelly marlstone.    From Wordnik.com.  [The Caravan Route between Egypt and Syria] Reference

Thus a marlstone train, dropping to sea level after crossing the Rockies, could function like a big hydroelectric plant, powered by rolling rock instead of falling water.    From Wordnik.com.  [High Country News - Most Recent] Reference