Gravel, Stone and Soil Delivery in American Canyon, CA

Hillside clay loam on a steep grade

The USDA soil survey maps Fagan clay loam, 15 to 30 percent slopes, at the center point of ZIP 94503. The Fagan series makes up 85 percent of the map unit. A grade in that range is steep for a drive and hard work for a wheelbarrow.^[1]

Fagan is rated well drained, because water can run downhill out of it. Its hydrologic group is C, though, so water soaks in slowly. On a steep slope, the rain that cannot soak in runs off fast and carries loose soil with it.^[1]

The top mineral layer is clay loam, a heavy, sticky soil when wet. Its shrink-swell rating in the top 100 cm is very high, at 9.8 percent linear extensibility. Ground like this swells after the winter rains and shrinks and cracks as it dries out.^[1]

The survey places paralithic bedrock at about 46 inches below the surface. Paralithic means soft, weathered rock that a digging bar can break with effort. Water that soaks down can stop on top of it and seep sideways along the slope.^[1]

The ground at the center point rises to about 240 feet above sea level.^[2]

A dry summer and a wet winter at the airport gauge

The NOAA normals station at Napa Co AP, CA, about 3 miles away, averages 20.2 inches of precipitation a year. Most rain in this part of California falls in the cool months, and summers are long and dry.^[3]

That pattern drives the clay cycle. The soil swells while it is wet in winter and shrinks through the dry season. Stone surfaces flex with that movement better than poured concrete, which is one reason gravel paths and drives suit this ground.^[1],[3]

The airport station counts 34 days a year with a low of 32 F or colder. Frost reaches the surface on some winter mornings, but it rarely lingers.^[3]

Its median last spring freeze is March 5. Its median first fall freeze is November 21. Most planting can happen after the March date, and fall mulch goes down well before the November one.^[3]

Building a drive across the slope

On a 15 to 30 percent slope, a gravel drive works best when it cuts across the hill or climbs it in gentle turns. A straight run up the fall line lets water race down the surface and strip it of stone.^[1]

Cut the bench into firm clay loam, then lay a heavy fabric on it. Build the base from Road Base or Crushed Concrete, compacted in thin lifts. Tilt the finished surface slightly into the hill so water runs to a ditch on the uphill side instead of over the downhill edge.^[1]

Top the drive with Driveway Gravel or 3/4" Crushed Stone. On the steepest sections, use angular stone, because it locks in place, while round stone rolls downhill under braking tires.^[1]

Every few lengths, set a shallow dip or a rubber water bar across the drive to turn runoff off the surface. Armor the spot where that water leaves with Riprap so it does not cut a gully down the slope.^[1]

Holding soil on a steep yard

Bare clay loam on a slope erodes in the first hard rain. Cover it with Brown Shredded Mulch or Black Shredded Mulch, which knits into a mat and holds on a grade better than loose chips.^[1]

Terraces turn a steep yard into flat beds. Build each one with a low wall and backfill behind it with Drain Rock next to the wall and Garden Soil in front. The stone lets water seeping along the slope pass through without pushing the wall over.^[1]

A dry creek of River Rock and Riprap can carry runoff down a slope without washing out. Bed the larger stones well into the clay, set them on fabric, and fill gaps with smaller River Rock.^[1]

Where water seeps out of a hillside after rain, a trench of Drain Rock or #57 Crushed Stone across the slope above a patio or a wall gives it a path around.^[1]

Choosing between Decomposed Granite and Pea Gravel

Decomposed Granite and Pea Gravel are the two most asked about path surfaces on hillside lots. Decomposed Granite is a blend of small grains and fines that sets into a firm, tan surface when wetted and rolled. Pea Gravel is small, round and loose.^[1]

On a slope, Decomposed Granite is the better pick. It packs into a surface that stays in place on a moderate grade and resists being kicked downhill. Pea Gravel creeps on any incline and suits only flat terraces and patios.^[1]

Each one needs a base and an edge. Lay fabric on the clay loam, add a thin compacted layer of Road Base, then spread the surface stone. On clay with very high swelling, cracks may show in a Decomposed Granite path after a dry summer. Wet the surface and roll it again to close them.^[1]

Beds and fill on heavy clay loam

Clay loam holds nutrients well but packs hard and stays wet in the rainy months. New beds do better when they are raised. Fill them with Garden Soil, or blend Topsoil with Compost, and keep the bed top a little above the clay around it so roots are not sitting in water after a storm.^[1]

Work Compost into any clay loam you plant directly, a few inches at a time, each season. Organic matter opens the soil and helps it drain. Dig only when the clay crumbles, since working it wet smears it into a dense layer.^[1]

Fill Dirt is useful to build up a flat pad on a slope or to fill behind a low wall. Compact it in thin lifts and keep it out of planting areas, since it carries little organic matter. Cover any exposed fill with mulch or plants before the wet season so it does not wash.^[1],[3]

Under a shed or a hot tub on this ground, a pad of Road Base topped with Stone Dust Screenings gives a level, firm footing that drains. Build it up on the downhill side rather than digging deeper into the hill.^[1]

Homes in ZIP 94503 and the state base rule

The Census counts 6,206 housing units in ZIP 94503, nearly matching the 6,131 inside the City of American Canyon. In the ZIP, 73 percent of homes are detached single-family houses, against 72 percent in the city.^[4]

The median home in the ZIP was built in 1997, and the city median is 1998. Owners live in 74 percent of occupied homes in ZIP 94503. Yards from that era often have beds and side paths ready for a refresh.^[4]

For state highways, Caltrans names Class 2 Aggregate Base, Section 26-1.02B, Standard Specifications (2026).^[5]