Published
What size gravel does an Island Park driveway need?
Base and surface are different jobs
Think structure, then skin. The base course exists to spread wheel loads over the subgrade and to bridge soft spots — so it's coarse, cheap, and thick, usually pit-run (straight from the pit, unscreened) or a large crushed ballast. The surface course exists to be driven on — so it's a crushed product with fines, the "minus" in names like three-quarter-minus, and those fines are the point: they fill the voids so the layer compacts into a crust that sheds water and holds its shape. Skip the fines and the top never binds; skip the base and the top slowly disappears into the ground it was asked to carry.
How deep the base goes is a frost question
The reason a driveway here needs real structure is the same reason footings here go deep. Fremont County writes its frost assumption down:
Minimum Frost Depth for Footings: The minimum frost depth for footings shall be 32 inches.
— Fremont County Ordinance 2005-02, Section 4 (retrieved 2026-08-12)
A driveway is not a footing and nobody is asking you to dig 32 inches of it. But a county that designs to Ordinance 2005-02's 32-inch figure is telling you what its winters do to the top of the ground, and frost that reaches that far is what turns a thin, under-drained gravel layer into washboard by its second spring. Depth and drainage are the same conversation. So is timing: cutting a driveway is excavation, so Idaho Code § 55-2205 (retrieved 2026-08-13) puts a locate ticket at least two business days ahead of the first bucket — see the 811 walkthrough for the window and the white paint.
Why round rock keeps failing driveways
River rock and screened round gravel look wonderful in a landscaping bed and behave like a driveway full of ball bearings — smooth faces can't interlock, so every tire pass pushes material out of the wheel path and the surface stays loose forever. Crushed rock is the opposite: fracture faces bite, fines pack, compaction makes it near-solid. In a place where the driveway spends half the year under a plow , that difference compounds — a locked crushed surface lets snow equipment skim clean, while loose rock gets broadcast into the snowbanks all winter and raked out of the lodgepole in June. (Whether the county ever plows your road is its own story — the driveway is yours either way.)
The five specifics that make a gravel bid real
- Materials by name — what's the base, what's the surface; "gravel" is not an answer
- Depth of each layer — tied to what the operator saw in your subgrade, not a brochure
- Compaction — priced per lift, or the layers are just piles shaped like a driveway
- Crown or cross-slope — water has to leave sideways; flat gravel becomes potholes
- The pit — which one, how far; hauling often costs more than rock, which is why the cost page treats haul distance as input number one
Common questions
What's the difference between base gravel and surface gravel?
Different jobs, different rock. The base course is coarse material — pit-run or ballast-sized stone — whose job is carrying load and bridging soft ground. The surface course is a crushed "minus" product, meaning it includes fines down to dust, whose job is locking into a tight, smooth crust you can drive, walk, and plow. One material can't do both jobs.
Why does a crushed "minus" product lock up when round rock doesn't?
Crushed rock has fractured faces that bite into each other, and the fines fill the gaps so the layer compacts into something near-solid. Round river rock is nature's ball bearings — smooth faces that never interlock, forever migrating out of the wheel path. It's fine as decoration; as a driving surface it stays loose indefinitely.
What is pit-run, exactly?
Material hauled straight from the gravel pit without screening or crushing — a natural mix of sizes, sometimes with cobbles. It's the cheap workhorse for building depth and a common base choice where hauling distance already dominates the price. What it isn't is a finished surface: expect a crushed cap over it before the driveway feels done.
Does the gravel choice change how the driveway plows?
Substantially. A tight, well-compacted crushed surface lets a plow or blower skim clean without harvesting gravel into the snowbank; loose or oversized rock gets scattered all winter and raked out of the trees in June. Island Park driveways spend half the year under snow-removal equipment, so the surface course is effectively winter infrastructure.
How much depth does a gravel driveway here need?
It's a bid item, not a universal number — subgrade decides. Firm, well-drained ground needs less structure; soft or wet ground needs more base doing more bridging. What matters is that the bid states its layers and depths explicitly, ties them to what the operator saw on your lot, and prices compaction rather than just dumping and spreading.
What should I ask for in a gravel driveway bid?
Five specifics: the base material and the surface material by name, the depth of each layer, whether compaction is included per lift, the crown or cross-slope that sheds water, and which pit the rock comes from — haul distance is often the biggest line in the price. A bid that just says "gravel driveway" hasn't decided any of these yet.
How deep should the base layer be?
Deep enough for the subgrade under it, which is why no honest answer arrives before someone stands on your lot. The useful frame is the county's own frost assumption: Fremont County Ordinance 2005-02 sets a 32-inch minimum frost depth for footings, so this is ground that moves. Firm, well-drained subgrade needs less base; soft or wet ground needs more, and needs the drainage fixed first. What you want in writing is the depth per layer and the reasoning behind it.
Do I need a locate before regravelling a driveway?
If any of it involves digging rather than laying material on top, yes. Idaho Code section 55-2205 sets the same window for a driveway cut as for a foundation: notice to the one-number service at least two business days and no more than ten before work starts, with the path pre-marked in white. Regravelling an existing surface without excavating is a different case — but the shallow-work exemption in section 55-2210 only applies where there is no reason to believe a utility runs within the depth you are working.