To make it even more confusing, pea gravel is technically a type of river rock, and they have a lot of similarities, but they are different size grades. Pea gravel usually sells for around $15 to $75 per cubic yard, while river rock costs $60 to $240 per cubic yard, depending on size. Both pea gravel and river rock are either artificially tumbled or collected from old streams, glacial deposits, and ancient river beds, where they where once polished smooth by moving water. Pea gravel and river rock can both have a lot of color variation between the stones, and those colors tend to look most dramatic when wet. Despite these similarities, they can have very different uses, so it's important to know what size pea gravel or river rock you need before placing an order.