Gravel, Rock and Garden Soil Delivery in Concord, CA

Silty Clay Loam on the Valley Floor

Sycamore silty clay loam, 0 to 2 percent slopes, MLRA 17, is the map unit the USDA soil survey shows at the center point of ZIP 94518. Silty clay loam is a fine, smooth soil, rich enough for gardens and heavy enough to stay sticky after a winter storm.^[1]

Flat ground with a fine texture drains slowly through the soil itself. Water from a roof or a patio spreads out across a level yard instead of running away, and a low corner can stay soft for days after the rainy season starts. Planning where storm water goes is the first step for any patio or path.^[1]

Fine soils also pump up into a base when they get wet and carry traffic. A woven geotextile laid between the soil and the first layer of stone keeps the two apart, and it is the single change that does the most for a gravel drive or patio on silty ground.^[1]

Gardeners have the easier job here. Silty clay loam holds water and nutrients well, so a vegetable bed needs some Compost to loosen it rather than a full replacement. Work the amendment in while the soil is damp but crumbly, never while it is wet and smearing.^[1]

Alluvium Below the Yard

The USGS state geologic map puts Quaternary alluvium and marine deposits at the ZIP's center point, a mix of coarse alluvium and fine alluvium. Alluvium is sediment laid down by moving water, so layers of silt, sand and gravel can alternate a few feet down.^[2]

A trench for a drain line or a deep planting hole may cross from fine silt into a coarser, sandy layer that drains much faster. Where you find one, a drain line or a dry well that reaches it moves water away far better than one that stops in the silt above.^[2]

The USGS elevation service reads 70 feet above sea level for the ground at the mapped center of the ZIP.^[3]

Coarse layers in alluvium can also hold stones and cobbles that stop a post-hole digger cold. Keep a pry bar handy for fence and deck footings, and backfill around posts with gravel so water drains away from the wood.^[2]

Wet Winters, Dry Summers at Buchanan Field

The NOAA normals station at Concord Buchanan FLD, CA, about 3 miles away, averages 16.1 inches of precipitation a year. Nearly all of it arrives in the cool months, and summers pass with almost no rain at all.^[4]

That pattern shapes the yard in two ways. In winter, fine silty soil turns soft and slow to drain, so paths and pads need a firm, drained base. In summer, the same soil dries hard, and plants rely on irrigation and mulch to hold moisture.^[1],[4]

Lows of 32 F or colder occur on 8 days in an average year at Buchanan Field. A few cold mornings can nip tender plants, but freeze heave is not a real worry for a base.^[4]

The station's median first freeze date is December 14 and its median last freeze date is January 9. Frost-tender plants can go in after mid January and stay out until the cold spell in December.^[4]

A Gravel Patio on Fine Soil

Dig the patio area down a few inches and remove any soft topsoil. Lay a geotextile across the bottom, overlapping the seams. On silty clay loam that stays soft through winter, the fabric keeps the base from sinking and the soil from rising into the stone.^[1]

Compact several inches of Road Base or Crushed Concrete in thin lifts, wetting each one before it is rolled. Slope the base slightly away from the house. On flat ground, a fall of even a little over the width of the patio keeps winter rain from collecting on it.^[1],[4]

For the surface, Decomposed Granite packed in thin layers gives a firm, warm-toned patio that suits a dry garden, and 3/8" Crushed Stone gives a looser, faster-draining surface for a fire pit or a sitting area. Pavers on an inch of Concrete Sand are the third option and the easiest to keep level.^[4]

For state highway base work, Caltrans uses Class 2 Aggregate Base, Section 26-1.02B, Standard Specifications (2026).^[5]

Homes and Garden Beds

The Census counts 10,317 housing units in ZIP 94518, and 63 percent are detached single-family houses. Concord as a whole has 47,703 housing units, with 59 percent detached.^[6]

The median home in the ZIP was built in 1970, the same median year as the city. Owners occupy 69 percent of the ZIP's occupied homes.^[6]

A side yard on fine valley soil can take a gravel strip for bins, bikes or a garden shed. Dig a few inches, lay fabric, compact a thin layer of Road Base, and finish with 3/8" Crushed Stone or Stone Dust Screenings. The strip stays firm through the wet months, when a bare dirt path would turn to sticky mud underfoot.^[1],[2]

Silty soil forms a crust on top when it dries after winter rain, and water then runs off instead of soaking in. A few inches of Brown Shredded Mulch or Black Shredded Mulch stops that crust from forming and keeps the soil below cool and damp through the dry months.^[1],[4]

Raised beds filled with Garden Soil warm up earlier in spring and drain faster in a wet winter than the native ground. For in-ground beds, mix Compost into the top several inches each fall, and the silty clay loam will turn darker and looser over a few seasons.^[1]

River Rock or Decomposed Granite for a Dry Garden

A dry garden built around 16.1 inches of yearly rain at Buchanan Field needs a ground cover that looks good without water. River Rock gives a cool, rounded look that suits a dry creek bed, and it stays put in a winter storm. It is harder to walk on, so keep it to beds, swales and borders.^[4]

Plant pockets in a stone garden still need care in the first summer. Fill each pocket with Garden Soil, water it deeply while the plant roots, and top it with the same River Rock or a small ring of Brown Shredded Mulch. With frost on only 8 days a year at the station, most drought-tolerant shrubs settle in quickly once the first dry season is behind them.^[4]

Decomposed Granite works for the walking parts of the same garden. Packed over a compacted base, it makes paths and small sitting areas between plantings. On fine soil, lay fabric under it so the silt does not mix in and turn the path muddy each winter.^[1]