Three Rivers flagstone is an argillite stone with a swirl pattern of gold, tan, beige and plum unlike any other. Formed in the high altitude of the Sawtooth Mountains of Idaho, Three Rivers stone is a very hard material ideal for pool decks, driveways and walkways.  Sold 1 - 1-1/2" thick, 1' - 2' pieces. 115 sq.ft./ton coverage.