Gravel, Rock, Soil and Mulch Delivery in Sparks, NV

Voltaire silty clay and how it moves

The USDA soil survey maps the Voltaire-Truckee complex, drained, at the ZIP's center point, and the Voltaire series makes up 45 percent of that map unit. The word drained in the name means the ground was once wetter and has had its water table lowered, as happens on valley floors that were turned into farmland or neighborhoods.^[1]

The top mineral layer is silty clay, and the survey rates its shrink-swell as high, at 7.5 percent linear extensibility. Silty clay this active swells when it wets and shrinks hard as it dries, opening wide cracks in summer and heaving in spring. A rigid slab poured straight onto it can crack, and a gravel drive laid on bare clay can turn soft and rutted after a wet spell.^[1]

The survey calls the Voltaire soil moderately well drained and puts it in hydrologic group C, meaning slow infiltration. Water lingers near the surface after rain or snowmelt, so a base here needs to keep water off the clay and move it away quickly.^[1]

An old alluvial fan below

The state geologic map shows older alluvium and alluvial fan deposits under the center point, made of coarse alluvium and fine alluvium of Pliocene age. Alluvial fans form where streams leave the mountains and spread their load across a valley, dropping coarse gravel first and fine silt farther out.^[2]

That history explains why a deep hole near the center point may pass from silty clay into sandy or gravelly layers below. For most yard work, though, the clay on top is what counts, and it is the layer every base and bed must deal with.^[1],[2]

Builders working near the center point sometimes find those coarse fan gravels in a footing trench. Clean, rounded gravel below the Voltaire clay drains far better than the clay above it, and a dry well dug down into it can take roof water from a downspout.^[1],[2]

The ground at the survey point stands 4,400 feet above sea level.^[3]

A reading taken at a single mapped point on the valley floor describes ground height and nothing more. What a lot owner can use is the local fall of their own yard. Run a string line from the house to the far edge, and plan any gravel area to slope away from walls, because water sitting against a foundation on silty clay soaks in and swells the soil right where you least want movement.^[1],[3]

Cold nights, little rain and a late spring freeze

Weather normals come from the NOAA station at Sparks, NV, about 1 mile away. It averages 8.4 inches of precipitation and 6.8 inches of snow a year. That is a dry climate, and most of the year the silty clay stays hard and cracked.^[4]

The Sparks station counts 141 days a year with a low of 32 F or colder. On many of those days the afternoon warms above freezing, so damp ground can freeze and thaw over and over. Silty clay that holds water through a cold snap heaves as it freezes, which is the main reason a gravel base here needs to drain.^[4]

The station's median last spring freeze is May 1, and its median first fall freeze is October 10. Tender plants wait until after the May date, and base work goes best in late spring through early fall, when the clay is dry and firm.^[4]

A drive that holds up on swelling clay

Start by digging out the top layer of silty clay and any organic material, then shape the subgrade with a crown. Lay woven fabric across the whole area. On high shrink-swell clay, fabric is not optional: it keeps the clay from mixing into the stone as the ground heaves and settles.^[1]

Over the fabric, add a layer of #57 Crushed Stone or 1-1/2" Crushed Gravel to break the path water would take up from the clay, then build compacted Road Base in lifts on top. That open layer drains, so less water sits in the base to freeze. Crushed Concrete can replace Road Base and compacts just as firmly.^[1],[4]

Finish with 3/4" Crushed Stone or Driveway Gravel. Plowed or shoveled snow piles at the edges of a drive and melts slowly, so give those edges a strip of Drain Rock that carries melt away from the base instead of letting it soak into the clay.^[1],[4]

High desert beds and dry yards

With 8.4 inches of yearly precipitation at the Sparks station, most plants need help holding water, and silty clay is hard for roots to break through once it dries. Raised beds filled with Garden Soil give plants a loose, workable root zone. In the ground, blend Compost into the clay to open it up.^[1],[4]

Mulch is valuable on both ends of the year. Brown Shredded Mulch or Wood Chips slow evaporation in summer and insulate roots against frost heave in winter. Spread a fresh layer after the median first fall freeze of October 10 to protect perennials through the cold months.^[4]

The 6.8 inches of yearly snow at the Sparks station rarely lingers, but when it melts on group C clay it has nowhere to go quickly. Keep beds a little above the surrounding grade and leave a path of River Rock or Drain Rock where meltwater from a roof edge can drain away from the plants.^[1],[4]

Many yards here use stone in place of lawn. Decomposed Granite makes a firm floor for paths, while River Rock and #57 Crushed Stone suit dry beds and borders. On swelling clay, lay fabric under any stone area so the clay does not push up through it over time.^[1]

Decomposed Granite or River Rock for a dry garden

Two stones lead most dry-garden plans in the ZIP: Decomposed Granite for the parts you walk on and River Rock for the parts you look at. With so little rain at the Sparks station, either one stays clean with no watering at all, but they ask different things of the silty clay underneath.^[1],[4]

Decomposed Granite packs into a near-solid floor, so it needs a firm, even base. On high shrink-swell clay, put fabric down, then two or three inches of compacted Road Base, then the Decomposed Granite rolled in thin lifts. Without that base, the clay below cracks in summer and the cracks show through the path. River Rock is far more forgiving. It sits loose on fabric, shifts a little as the ground moves and never shows a crack. It does not suit a path, since rounded stones roll underfoot, but it makes a handsome dry bed, border or swale.^[1]

A blend of the two, Decomposed Granite paths edged with River Rock, gives a yard a usable floor and a place for snowmelt to soak in.^[1]

Homes in ZIP 89431 compared with Sparks

The Census counts 17,202 housing units in ZIP 89431. Detached single-family houses make up 48 percent of them, and owners live in 45 percent of the occupied homes.^[5]

Sparks as a whole holds 45,898 housing units, and 62 percent are detached houses. The median home dates from 1973 in the ZIP and 1993 across the city. With a large share of rentals and attached homes in the ZIP, many projects are modest: a refresh of stone in a side yard, Decomposed Granite for a patio, or soil for a few raised beds.^[5]