Synthetic River Rock - Black Obsidian | Decorative, Plastic Landscaping Stones by Thor Decor - Made in the USA Thor Decor River Rocks are proudly made in the USA using recycled poly product. These decorative plastic landscaping rocks are a lightweight alternative to real stones. River Rocks are designed for use in plant containers and landscaping projects. They do not stir up dust, dirt, or allergens, making them an ideal alternative to dry, fibrous dressings. Their clean, decorative design will not add unsightly dirt or debris to your dcor. Thor Decor River Rocks allow you to cover more square footage per pound than regular stones. Pound-per-pound, our stones cover nearly 2.5 times more surface area than real river rocks. Plastic River Rocks decrease weight stress placed on planting containers and allow for hassle-free soil sampling. 4 lbs of River Rocks cover approx. 2 sq. ft. in a single layer or 1/2 to 3/4 sq ft. at a 2" depth.