Profile: Columbia River Stone offers building materials. We offer flagstones, stepstones, boulders, wall rocks, dimensional stones, gravel and pebbles. The iron mountain flagstone has a high iron content that brings out rust colored accents on this blue-black slate. Our 1" minus flagstone covers approximately 200 sq ft per ton, and can be veneered into countertops & fireplaces or mortared patios. The windswept boulders are glacially sculpted and naturally covered with a rich layer of mosses & lichens. They are used for constructing water-features of all sizes, and can also be used for boulder walls or stand alone accents to landscapes.