Gravel, Stone and Soil Delivery in Boise, ID

Foothill loam on steep ground

The soil survey maps the center point of ZIP 83702 as Picketpin-Van Dusen complex, 25 to 65 percent slopes. Picketpin is the main series, at 50 percent of the unit. Ground this steep belongs to the foothills, and many lots in the ZIP lie on gentler land below the mapped point.^[1]

Picketpin is rated well drained and sits in hydrologic group B, with moderate infiltration. Its top mineral layer is loam, an even mix of sand, silt and clay that holds water and still drains. Shrink-swell in the top 100 cm is moderate, at 5 percent, enough that a base laid on bare loam can move a little between wet and dry seasons.^[1]

The geologic map shows Sedimentary rocks associated with flood basalts beneath the point, a Burdigalian unit of mixed clastic rock, basalt and rhyolite. Weathered basalt and sediment break into angular rubble, which shows up in cuts and test holes on foothill lots. The ground at the center point stands 3,500 feet above sea level.^[2],[3]

Basalt rubble from a test hole is not a problem to dig out. Angular pieces like that compact well and can stay in the subgrade. Soft, fine loam is the layer to watch, because it holds melt water and softens under a load.^[1],[2]

Snow, frost and a dry year at Boise 7 N

Boise 7 N, ID, about 5 miles away, is the NOAA normals station for this ZIP. It records only 18.0 inches of precipitation a year, yet 57.4 inches of snow. Lows fall to 32 F or colder on about 125 days.^[4]

Spring frost hangs on late at that station, with a median last freeze of May 17. Fall frost returns early, with a median first freeze of October 12.^[4]

That mix of dry air and deep snow makes spring melt the wettest time of year for a gravel surface. Snow piled along a drive melts slowly and soaks the edges for weeks, and nights below freezing turn that water to ice inside the base. A drive that sheds melt quickly suffers far less damage.^[4]

Freezing nights come on so many days that a gravel surface goes through many freeze and thaw cycles each year. Stone that sits dry handles those cycles with little change. Stone sitting in water is lifted a little each time, so drainage is the first thing to get right.^[4]

A foothill driveway built for winter

On a sloped lot, cut the subgrade to a steady grade with no dips where melt can pool. Remove topsoil and soft loam, then lay fabric over the loam to keep the base from mixing with it as the ground freezes and thaws. On a steep drive, a cross slope toward a ditch on the uphill side moves water off the surface before it gains speed.^[1]

Build the base in compacted lifts of Road Base. It locks together and stays firm under the weight of plows and cars. Finish with Driveway Gravel or 3/4" Crushed Stone, both of which give traction on a grade. Avoid Pea Gravel on any slope: it rolls and piles at the bottom.^[1]

Line the ditch with 1-1/2" Crushed Gravel or River Rock and set Riprap where it empties. Plow with the blade raised a little so the surface stone stays on the drive and does not end up in the lawn.^[4]

Snow storage needs planning too. Leave a wide shoulder of grass or River Rock where the plow can push snow, on the low side of the drive if you can. Melt from that pile then runs away from the stone rather than across it.^[4]

Ice is the other winter hazard on a sloped gravel drive. A clean, angular top stone like 3/8" Crushed Stone gives boots and tires something to bite into, and it can be raked back into place after the thaw.^[4]

Retaining walls and terraces

Steep lots in the foothills often need retaining walls to make flat space for a patio or a garden. Behind each wall, backfill with Drain Rock or #57 Crushed Stone wrapped in fabric, and lay a perforated pipe at the base to carry water out the end. Snowmelt behind a wall that cannot drain freezes and pushes the wall outward.^[1],[4]

Under the first course of block, a compacted pad of Road Base gives the wall a level, solid footing. Fill the terraces with Topsoil or Garden Soil for planting. A few inches of Compost mixed in gives new plants a good start in the loam.^[1]

Small walls under knee height can be built from stacked stone with a gravel backfill and no mortar. Set the base course on Road Base, lean each course slightly into the slope, and fill every gap behind it with #57 Crushed Stone.^[1]

Water-wise yards and beds

With only 18.0 inches of precipitation a year at the station, most of it as snow, summer yards dry out fast. Mulch makes the biggest difference. Wood Chips or Shredded Mulch over beds slow evaporation and keep soil cool. Decomposed Granite or 3/8" Crushed Stone makes paths that need no water at all.^[4]

Plant tender crops after the May 17 median last freeze. The growing window before the October 12 median first freeze is short, so raised beds filled with Garden Soil help by warming up faster in spring.^[4]

Gravel gardens of River Rock or Pea Gravel around drought-tolerant plants look tidy all year. Under the stone, a layer of fabric keeps weeds down, and the well-drained loam carries the occasional summer storm away.^[1]

Fire-wise landscaping is worth thinking about on a foothill lot. A band of crushed stone or Decomposed Granite close to the house keeps dry mulch and grass away from the walls, while mulch and plants fill the yard farther out.^[1]

Water new plants deeply and less often in summer. Loam with moderate infiltration takes a slow soak well, and mulch on top keeps that water in the root zone for days.^[1]

Homes in ZIP 83702

The Census counts 13,159 housing units in ZIP 83702. Detached single-family houses make up 55 percent of them. The median home was built in 1969, and owners live in 51 percent of the occupied homes.^[5]

Older houses often have drives and walks that have settled over the years. Rebuilding one on a fresh, compacted Road Base and a clean layer of surface stone usually fixes both the ruts and the puddles.^[5]

Detached houses are just over half of the homes in the ZIP, and the rest are apartments, townhomes and condos. Shared lots often need small, tidy fixes: a stone path to a side door, a strip of River Rock along a walk, or a layer of fresh mulch in the front beds.^[5]