Gravel, Rock and Soil Delivery in Yuma, AZ

Holtville clay under a desert sky

The USDA soil survey places Holtville clay at the ZIP's center point, and the Holtville series makes up 100 percent of that map unit. Its top mineral layer is clay, which surprises people who picture a desert floor as loose sand. Clay particles are flat and tiny, so they pack into a dense crust when dry and turn sticky the moment water reaches them. A gravel job on this kind of ground starts with a firm, separated bed, or the clay slowly works its way up into the stone.^[1]

Shrink-swell in the top 100 cm rates high, at 7.5 percent linear extensibility. Holtville clay grows when it gets wet and pulls back as it dries, and in strong desert heat the drying half of that cycle comes quickly. Wide cracks can open across bare clay in summer and close again after irrigation. Poured slabs feel the movement as cracking and lifting. A loose stone surface rides through it, because each piece can shift slightly and settle back into place.^[1]

The survey calls the soil well drained and puts it in hydrologic group C, slow infiltration. Those two ratings describe different things. Well drained means water does not stay trapped in the profile for long periods. Group C means rain enters the surface slowly, so a sudden downpour runs across the top before much of it soaks in. Grading and edging that steer surface water do more for a yard on this soil than counting on the clay to swallow a storm.^[1]

River sediment and a low valley floor

Below the soil, the geologic map shows Holocene river alluvium at the center point, a young deposit of sand, gravel, silt and clay left by moving water. River sediment changes over short distances, so one dig can hit a sandy lens while another a few steps away turns up solid clay. Look at what comes out of a footing or trench before you pick the base material for it.^[2]

Survey elevation for the mapped center point comes out at 120 feet above sea level. On a level lot, build a slight fall into any patio, path or parking pad so that runoff from a cloudburst has somewhere to go besides the edge of the house.^[3]

Very little rain and a lot of sun

Weather normals come from the NOAA station at Yuma Quartermaster Depot, AZ, about 4 miles away. It averages 3.2 inches of precipitation a year and 0.0 inches of snowfall. With so little moisture, dust and wind wear on a gravel surface more than washouts do. The fines in Road Base can lift away as dust once the top dries out, so a clean cap of crushed stone over the compacted base keeps a driveway neater.^[4]

The station records 4 days a year when the low drops to 32 F or colder. Its median last freeze date is January 8. Its median first freeze date is December 28. Frost heave does not shape a driveway design with so few cold nights, though tender plants may want a cover on the coldest evenings around the turn of the year.^[4]

Heat steers material choices as much as rain does. Dark stone and dark mulch soak up afternoon sun and hold it into the evening, while pale rock reflects more light. Black Shredded Mulch still has a place in a shaded bed, but a dry climate dries out and breaks down wood mulch quickly, which is why so many desert yards use rock cover instead.^[4]

Desert yards with Decomposed Granite and rock

Decomposed Granite suits paths and seating areas in a dry place. It packs into a firm, earthy surface that drains through its own grains and stays put underfoot. Spread it over a scraped and compacted bed, mist it lightly, then roll or tamp it. On clay ground, a layer of fabric under the Decomposed Granite keeps the two from mixing when the clay swells after watering.^[1]

River Rock and 3/4" Crushed Stone cover planting areas without the yearly top-up that bark needs. They let drip lines reach the roots, shade the clay surface and cut down on the cracking that bare ground shows in summer. Along a walk, rounded River Rock looks softer, while angular crushed stone locks in place and resists being kicked onto the path.^[1],[4]

For planting holes, blend Compost or Garden Soil with some of the native clay instead of filling the hole with soft mix alone. A pocket of loose soil inside heavy clay collects irrigation water like a bowl and can drown roots. A wider hole with blended backfill lets roots spread outward. Topsoil works for raising a bed above the surrounding grade so it sheds water rather than collecting it.^[1]

Sand has its own jobs in a desert yard. Playground Sand fills a play area with soft, washed grains that do not cake hard in the heat. Mason Sand is finer and suits a smooth bed under flagstone or a mortar mix for a garden wall. Fill Sand is the plain bulk choice for raising a low area that will be covered later. Keep each one away from the clay with fabric, or the two will blend into a sticky layer the first time the sprinklers run.^[1]

A parking pad built for swelling clay

Scrape off loose surface material and check the clay underneath. Shape it with a slight crown or a fall to one side, then compact it while it is damp rather than wet. Lay woven fabric over the whole area. On a soil with high shrink-swell this layer does much of the work, because it stops clay from pumping up into the base each time the ground gets wet.^[1]

Add Road Base in thin lifts and compact each one hard. The angular pieces and fines lock into a stiff layer that spreads wheel loads across soft spots in the clay. Crushed Concrete behaves the same way and makes sense for a work yard or an RV pad. Top the base with 3/8" Crushed Stone or Driveway Gravel, spread thin enough that tires bite through to the firm layer instead of rolling in loose stone.^[1]

Homes in ZIP 85364

The Census counts 32,534 housing units in ZIP 85364. Detached single-family houses make up 55 percent of them, close to the 56 percent share across Yuma. The median home in the ZIP was built in 1983, several years before the 1990 median for the city as a whole. Owners live in 60 percent of the ZIP's occupied homes. Yuma as a whole counts 44,663 housing units.^[5]

A mix of houses, yards and side lots means plenty of small jobs. Common requests include a fresh top layer on a settled driveway, rock for a front yard that no longer gets watered, and a load of Fill Dirt to level a low corner before new pavers go down.^[5]