Rock, Gravel and Mulch Delivery in Round Rock, TX

Silty clay over soft chalk rock

At the center point of ZIP 78664, the USDA soil survey maps Austin silty clay, 1 to 3 percent slopes. The Austin series makes up 90 percent of the map unit. The top mineral layer is silty clay, sticky when wet and hard as brick when dry.^[1]

Dark, clay-rich soils like Austin are fertile but stubborn. Dig them when slightly moist, never soaking wet or bone dry, and they break apart cleanly.^[1]

The survey rates the soil well drained, yet it places it in hydrologic group D, very slow infiltration and high runoff. The reason sits in the profile: paralithic bedrock at about 29 inches, a soft rock layer that water passes through only slowly. Rain soaks the clay above it, then runs off once that thin layer is full.^[1]

Shrink-swell in the top 100 cm is moderate, at 5.1 percent. The clay swells and cracks with the seasons, though less than the heaviest clays. On the USGS state geologic map, the center point lies on Austin Chalk, a Late Cretaceous unit of marlstone, chalk and claystone. The ground at the center point stands 750 feet above sea level.^[1],[2],[3]

What the Great Hills station records

The closest NOAA normals station is Austin Great Hills, TX, about 10 miles away. It averages 37.1 inches of precipitation a year, and the low reaches 32 F or colder on 27 days in an average year.^[4]

That station's median last spring freeze is March 11, and its median first fall freeze is November 20. The growing stretch between them is long, and frost rarely threatens a gravel surface for more than a few nights at a time.^[4]

Rain in this part of Texas can come in sudden, heavy bursts. On a group D soil with rock not far down, that water moves across the surface instead of soaking in, and it carries loose gravel and bare soil with it. Design every surface to shed water to a planned spot.^[1],[4]

Summer heat bakes silty clay hard and opens wide cracks. Water a dry bed slowly so it soaks into the cracks instead of running off, and keep mulch on bare soil through the hottest months.^[1]

A driveway on shallow clay over rock

Dig out the dark topsoil and soft clay. With rock at about 29 inches in the survey profile, a driveway excavation will rarely reach it, but a deeper trench for a pipe or a footing may. Soft, paralithic rock can usually be broken with a bar or a digging machine.^[1]

Lay a woven fabric over the clay so it cannot work up into the stone, then compact Road Base or Crushed Concrete in thin, wetted lifts. Finish with Driveway Gravel, 3/4" Crushed Stone or Asphalt Millings. Crown the surface and add a shallow swale along the downhill side to catch fast runoff.^[1]

TxDOT names Flexible Base under Item 247 in its Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges (2024), the item for the stone layer it places under state pavement.^[5]

A home drive does not have to meet that item, but the same approach serves it well: angular stone of mixed sizes, compacted hard, kept dry underneath. A drive built this way rides out the swelling and shrinking of moderate clay far better than gravel dumped on bare dirt.^[1]

A gravel drive on slopes of 1 to 3 percent drains well when the crown and the swale work together. Check it after the first big storm and add Driveway Gravel wherever water has started to cut a channel.^[1]

Decomposed Granite or Stone Dust Screenings for a path

For garden paths and patios, two fine stone surfaces are the usual picks. Decomposed Granite is a gritty, earth-toned stone that binds when misted and rolled into a firm, natural surface. Stone Dust Screenings are finer crushed rock that packs even tighter and smoother, with a gray tone.^[1]

Either one needs the same groundwork on silty clay: fabric, a compacted base of Road Base, a firm edge, and a slight cross slope. Without fabric, the clay pushes up into the fines after every wet season. Decomposed Granite suits a relaxed, natural look, while Stone Dust Screenings make a smoother walk for wheels and strollers.^[1]

In a climate with only 27 freezing nights in an average year at the station, both surfaces hold up for years with an occasional top-up. Heavy runoff is the bigger threat, so keep downspouts and swales from aiming across a fine-stone path.^[1],[4]

Patios follow the same plan. Flagstone set in Decomposed Granite or Stone Dust Screenings over a compacted base makes a casual patio that drains through its joints, and it handles the small movements of moderate clay better than a poured slab.^[1]

Runoff, beds and shallow soil

Fast runoff off silty clay can cut channels through beds and lawns. Line those paths with River Rock or #57 Crushed Stone to form a dry creek bed that slows the water and looks deliberate. At a steep drop, a few pieces of Riprap hold the bottom of the channel in place.^[1]

Dry wells struggle where soft rock lies about 29 inches down, because water has nowhere to go. A French drain with Drain Rock around a perforated pipe, carried to the street or a lower yard area, works better.^[1]

Shallow clay over rock limits root depth. Raised beds filled with Garden Soil give vegetables and shrubs more room. Compost worked into the top of in-ground beds loosens sticky clay and helps it drain. Spread Brown Shredded Mulch, Black Shredded Mulch or Wood Chips after the March 11 median last freeze, and refresh it ahead of the November 20 median first freeze.^[1],[4]

Topsoil spread a few inches deep over a thin lawn gives grass a better root zone over the clay. Fill Dirt raises low spots that collect water, compacted in layers before the Topsoil goes on.^[1]

Pea Gravel makes a cool, soft floor for a seating area under a shade tree, laid over fabric with a firm edge so it stays out of the lawn.^[1]

Homes in ZIP 78664

The Census counts 24,497 housing units in ZIP 78664. Detached single-family houses make up 63 percent of them, and owners live in 54 percent of the occupied homes. The median home in the ZIP was built in 1997.^[6]

For Round Rock as a whole, the Census reports 51,143 housing units, with detached houses at 64 percent. The city's median year built is 2002.^[6]

Houses from the late nineties often carry their first landscaping, now due for an update. Typical projects include rock beds in place of struggling turf, a gravel pad for a trailer or boat, and fresh mulch around trees that have filled out.^[6]

Yards in the ZIP often hold trees that have grown large over the years. Mulch rings around those trees, and rock beds where shade has thinned the grass, are common orders.^[6]