granite- wilson boulder Wilson Boulders, or Rip Rap are clean crushed granite. Sizes run from 1' to 5' in diameter. These boulders can be used as part of a landscape theme or in engineering projects such as bank, river or coastline stabilization. All sizes of Cal Trans Specification Rip Rap up to 10 ton are available daily. This type of rock is typically gray in color. AVAILABLE SIZES DESCRIPTION THICKNESS COVERAGE AREA Landscape Boulders 1' – 5' dia 6 – 12 sf /ton