MIGHTY109 San Benito Blue River Cobbles 40 pounds R.R. Special Mighty109 San Benito Blue River Cobbles 40 pounds R.R. Special Beautiful range of dark blue, grey, and brown color tones. Great accent in ponds, waterfalls, pathways, patios, aquariums and more. Stones are rounded, and about 1-3 inches in size on average. 40 Pounds - R.R. Special. Engine 109 The Bulk Depot