River rock is heavier than most people expect — 2,500 to 3,500 pounds per cubic yard — and because it is usually bought for looks rather than function, running short partway through a bed is very visible.
Depth
Two to three inches covers the ground properly. Because the stones are larger than crushed gravel, a thin layer lets the fabric or soil show through between them, which defeats the point.
Larger decorative stone — three inches and up — needs proportionally more depth to look intentional rather than scattered.
Put fabric under it, and know the trade-off
Landscape fabric under river rock keeps the stone from working down into the soil, which is the main reason rock beds look thin after a few years.
The trade-off is that organic matter still collects on top of the fabric over time, weeds root in that layer, and pulling them is harder because the fabric is in the way. Plan on blowing debris out of a rock bed once or twice a year.
Ordering
Colors vary between deliveries because it is a natural product. If a bed is large enough to need two loads, order them together rather than months apart.
Bagged river rock is generally 0.5 cubic feet — expensive per unit volume, but sometimes the only option if a truck cannot reach the site.
Size changes how it behaves
River rock is sold by size range, and the size decides what it is good for far more than the colour does.
Three quarter to one inch is the general landscape size — it stays put, it is comfortable enough to walk on, and it does not disappear into the soil.
Two to four inch and larger is for drainage features, dry creek beds and areas nobody walks on. Small sizes under half an inch behave like coarse gravel and migrate into the soil within a couple of seasons.
Rock is permanent in a way mulch is not
Mulch breaks down and gets topped up or replaced. Rock does not break down, and that cuts both ways.
It never needs replacing, which is the selling point. But it also collects leaves and soil in its gaps until organic matter builds up between the stones, weeds root in that, and the only remedy is to lift and wash the rock or to remove it.
Removing an established rock bed is heavy, slow work — it is the reason to be sure about the design before the delivery arrives.