Excavation
Quarry Spalls vs. Riprap: Choosing Big Rock (Oregon)
Cojo
June 19, 2026
6 min read
Quarry spalls vs riprap in Oregon comes down to one question: are you stabilizing ground you will build on, or armoring a slope against erosion? Quarry spalls are large angular rock used to bridge soft, muddy subgrade and create a stable working pad. Riprap is large rock placed to protect slopes, banks, and channels from washing out. They look similar in the pile, but they do different jobs. If you are trying to build a road or pad over soggy ground, you want spalls. If you are holding a hillside or streambank against water, you want riprap.
Both products are large rock, often the same basalt out of an Oregon quarry, but they are specified for opposite purposes. Confusing them leads to either a pad that still pumps or a slope that still washes out. The litmus test is straightforward:
The excavation materials and hauling guide covers the full menu of rock and aggregate. This page focuses on telling these two big-rock products apart.
Quarry spalls are large, angular fragments of rock. Their job is soft-soil stabilization: dumped and tracked into soggy, weak subgrade, they bridge the mud and form a firm working platform. The angular faces lock together, and the size lets them press down into soft ground and create a stable base where a truck or machine would otherwise sink.
Typical uses:
In Oregon, this is a wet-season staple. Soggy Willamette Valley clay subgrade in winter is exactly the condition spalls were made for, and basalt spalls from Central Oregon quarries are common in the high country.
Riprap is large rock placed to armor a surface against moving water. Instead of being driven into soft ground to bear load, it is laid on a slope, bank, or channel to absorb the energy of flowing or splashing water so the soil underneath does not erode.
Typical uses:
Our riprap erosion rock explained piece goes deeper on sizing and placement for erosion control.
Both products usually go over a geotextile fabric, but for related reasons. Under spalls, fabric separates the rock from the soft subgrade so the mud does not pump up and swallow the stone, preserving the stabilizing platform. Under riprap, fabric keeps the soil it protects from washing out through the gaps between rocks. In both cases, the fabric is what makes the rock last; skip it on soft or erodible ground and the rock slowly disappears into or out of the soil.
| Factor | Quarry Spalls | Riprap |
|---|---|---|
| Main purpose | Stabilize soft subgrade | Armor against water erosion |
| How it works | Bridges mud, bears load | Absorbs water energy |
| Where it goes | Pads, access roads, work platforms | Slopes, banks, channels, outlets |
| Fabric below | Separates from soft soil | Holds protected soil in place |
| Litmus test | Building on it | Protecting against water |
Large rock is sold by the ton, delivered, and the price moves with quarry distance and trucking.
Industry Baseline Range: large quarry rock such as spalls and riprap commonly runs roughly $30 -- $90+ per ton delivered, with dump truck delivery adding $250 -- $750+ per load depending on distance, plus geotextile fabric as a separate per-square-foot line. These are industry baseline ranges for planning only -- actual pricing depends on site conditions, soil, access, depth, haul-off, and current market conditions. Get a site-specific quote.
Long haul distances from the quarry can run trucking 2 to 3 times the rock itself, especially on remote rural lots. The fabric and the labor to place and key in the rock add to the total. The cheapest delivered ton is not always the cheapest installed job once trucking and placement are counted.
Ordering the right rock is only half the job; how it goes in decides whether it performs. Both spalls and riprap are placed, not just dumped, and the technique differs because the jobs differ.
For quarry spalls building a working pad, the rock is spread and worked into the soft subgrade so it bridges the mud and forms a continuous, stable platform. Over fabric, the angular pieces lock together as equipment tracks over them, pressing the platform down to firm bearing. Done right, you get a surface a loaded truck can cross; done carelessly, with too thin a layer or no fabric, the mud pumps up through the gaps and the platform never sets up. On the worst ground, a thicker lift of spalls is what gets the job to stable.
For riprap armoring a slope or channel, placement is about coverage and keying. The rock is laid to a designed thickness so there are no thin spots where water can get under it, and the edges are keyed in, tucked below grade or anchored, so flow cannot peel the armor back from the bottom or sides. A graded mix of sizes fills the voids between the largest stones so soil cannot wash out between them. Riprap that is simply piled rather than placed and keyed tends to fail at the edges and unravel.
In both cases, the fabric beneath and the care of placement are what turn a load of rock into a working solution. This is why big-rock work is sold and quoted as an installed job, the delivered tonnage is just the raw material. Whether you are stabilizing ground or armoring against water, ask how the rock will be placed and keyed, not just how much is coming.
Quarry spalls stabilize soft ground you will build on; riprap armors slopes and channels against water. Use the litmus test, lay fabric underneath, and size the rock to the job. For base and aggregate questions beyond big rock, see our road base aggregate explained piece. Cojo supplies and places rock statewide. See our excavation services and request a free estimate.
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