Gravel, Decorative Rock and Soil Delivery in Sunnyvale, CA

Clay Under the Pavement

The USDA soil survey maps Urbanland-Hangerone complex, 0 to 2 percent slopes, drained, at the ZIP's center point. That survey counts 70 percent of the map unit as urban land, meaning ground already paved or built over. The main named soil, Hangerone, makes up 25 percent.^[1]

Where the native soil does show, its top mineral layer is clay, and the survey calls it poorly drained, in hydrologic group C. Rain soaks into that soil slowly, so water stands on it after a storm. Shrink-swell in the top 100 cm rates very high, at 10.5 percent linear extensibility, which means the clay expands noticeably when wet and pulls back and cracks as it dries.^[1]

Below the soil, the USGS state geologic compilation shows Quaternary alluvium and marine deposits at the center point, made up of coarse alluvium and fine alluvium. Alluvium is material laid down by moving water, so layers of sand, gravel and silt can sit stacked under the clay. A deep hole may hit a coarser band, but the top layer is where a base or a bed has to be planned.^[2]

Building a Base on Swelling Clay

Clay with very high shrink-swell is the main reason patios crack and pavers rock in this part of the valley. The fix is distance and drainage. Dig the clay out to a firm layer, lay a woven fabric, and build up a thick base of Road Base in thin lifts, compacting each pass. The stone spreads the load and keeps the clay below at a steadier moisture level.^[1]

For a side-yard walk or a patio of loose stone, Decomposed Granite packs into a firm, natural surface over that compacted base. For a driveway, 3/4" Crushed Stone or Driveway Gravel on top of the base holds up to tires. Keep a gentle fall away from the house, even on ground that only slopes 0 to 2 percent at the center point, so water never collects against the foundation.^[1]

Caltrans, the California Department of Transportation, names its aggregate base Class 2 Aggregate Base, in Section 26-1.02B of its Standard Specifications (2026). The state's road builders rely on graded crushed rock for the course under their pavement, and the same idea of well-graded, compacted stone carries over to a home drive.^[3]

Dry Winters and Rare Frost

Moffett Federal Airfield, CA, a NOAA normals station about 2 miles off, provides the nearest long weather record. It averages 13.4 inches of precipitation in a year, and its low drops to 32 F or colder on just 2 days in a typical year. The median last freeze date there is January 6, and the median first freeze date is December 23.^[4]

With so little frost, heaving is rarely an issue for gravel here. The bigger concern is the swing between dry months, when clay shrinks and cracks, and the rainy stretch, when it swells and holds water. Gravel surfaces that drain fast stay usable through both. A layer of mulch on beds keeps the soil from drying out and cracking in the warm months.^[4]

Low rainfall also favors gravel and rock over thirsty lawn in a lot of yards. A front yard of River Rock and Decomposed Granite, with planting pockets filled with Garden Soil, needs far less water than turf and still looks finished. Use fabric under the stone so weeds do not push through.^[4]

Small Lots, Shared Walls

The Census Bureau counts 10,146 housing units in ZIP 94085. A quarter of them, 25 percent, are detached single-family houses, and the median home in the ZIP went up in 1988. Owners live in 38 percent of the occupied homes there.^[5]

Across Sunnyvale the Census tallies 63,239 housing units, with 36 percent detached and a citywide median year built of 1976. In a ZIP full of townhomes and apartments, many orders are modest: a few tons of rock for a courtyard, mulch for shared planters, or sand for a play area. Gravel Valet handles small loads as readily as large ones.^[5]

Drainage on Flat Clay Lots

Flat clay holds water at the surface, so drainage work earns its keep here even in a dry climate. A French drain is a trench lined with fabric, filled with Drain Rock or #57 Crushed Stone, with a perforated pipe at the bottom where needed. It collects water from a soggy patch and carries it to a lower spot or the street.^[1]

Where downspouts empty onto clay, a splash bed of River Rock keeps water from carving a hole. A dry creek bed of River Rock with a few larger stones can carry winter runoff across a yard and look like a garden feature the rest of the year. Line it with fabric so the clay does not wash up into the rock.^[1]

For planting beds over clay, build up rather than down. Garden Soil and Compost mounded into raised beds drain better than amended clay and warm faster after the rainy stretch. A topping of Brown Shredded Mulch or Red Mulch holds moisture in through the dry season and keeps the surface from crusting.^[1]

Choosing Rock for Looks and Use

Decorative rock does two jobs in a dry valley yard: it replaces water-hungry lawn and it handles the occasional heavy rain without turning to mud. River Rock gives smooth, rounded stones in mixed tones that suit borders and creek beds. Pea Gravel is smaller and softer underfoot, a good fit for paths and seating areas. #89 Crushed Stone and 3/8" Crushed Stone are small angular chips that pack a little tighter than Pea Gravel and stay put better on a walk.^[4]

For the base of anything that carries weight, the angular grades matter more than looks. #57 Crushed Stone drains freely and makes a good layer under pavers or a shed floor where water needs to move. Road Base, with its mix of sizes and fines, compacts into a dense, stiff layer that resists rutting. On clay with high shrink-swell, a stiff, thick base is what keeps the surface level.^[1]

Many yards in the ZIP mix the two approaches: a compacted base and Decomposed Granite for the parts people walk on, and River Rock or mulch for the planted areas. Fabric under the stone in both zones keeps the clay from rising into it and keeps weeds from finding a gap. Edging of steel or stone holds each material in its own place.^[1]

Playground Sand is a common order too, for a sandbox or a play corner in a courtyard. Keep it in a framed bed with fabric underneath so it stays clean and does not mix with the clay. Mason Sand, a finer sand, is the one masons use for mortar and the one many people choose for setting flagstone joints.^[1]