PCC sells a wide variety of sand, gravel, topsoil, beauty bark, red cinders, lava rock, quarry rock, compost, nutra-mulch, etc. They are conveniently located on Highway 169 in Black Diamond (Look for the big yellow steam shovel on the highway). These guys are friendly and open Saturdays. You can buy as much product as you want, because it is on a weigh-in, weigh-out basis: you only pay for what you get. They also deliver any of their products, but many customers just show up in their pick-ups and trailers to buy lots of different landscaping products. They even have a great website with lots of photos.
Pros: Open Saturdays, buy any amount, friendly, family-owned
Cons: Only take cash or check, no credit or debit cards