Stone, Gravel, Soil and Mulch Delivery in Simi Valley, CA

Nacimiento silty clay loam on a slope

The USDA soil survey maps Nacimiento silty clay loam, 15 to 30 percent slopes, eroded, at the ZIP's center point, and the Nacimiento series fills 85 percent of that map unit. The word eroded in the name tells you some of the original topsoil has already washed off the slope, leaving a thinner, heavier layer behind.^[1]

The top mineral layer is silty clay loam, a fine, smooth soil that turns sticky when wet and hard when dry. The survey rates its shrink-swell as moderate, at 4.5 percent, so it swells a little after rain and shrinks back over the dry months.^[1]

The Nacimiento soil is rated well drained, but it sits in hydrologic group C, with slow infiltration. The survey also lists paralithic bedrock at about 26 inches, a soft rock layer close to the surface. On a slope, that means rain soaks in slowly, runs off quickly, and can travel along the top of the rock layer before seeping out lower down.^[1]

Dry normals at the Newhall station

Weather normals come from the NOAA station at Newhall 5NW, CA, about 9 miles away. It averages 16.8 inches of precipitation and 0.1 inches of snow a year. Most of that rain falls in a few storms, and on slow-draining, sloped ground a single storm can move a lot of soil.^[2]

The Newhall station counts 1 day a year with a low of 32 F or colder. Frost plays almost no part in planning a base or a bed. The real forces here are dry heat and the occasional hard rain.^[2]

The ground at the survey point stands 1,160 feet above sea level.^[3]

The Newhall normals list just 0.1 inches of snow a year, so a gravel surface on a Simi Valley hillside never has to stand up to a plow or a winter of meltwater. Heat and sun are what wear down mulch and fade stone here, so pick materials that hold their color and replace mulch as it breaks down.^[2]

Holding a slope with stone and mulch

On 15 to 30 percent slopes with slow infiltration, bare soil is the first thing a storm takes. Cover slopes with Brown Shredded Mulch or Wood Chips, which slow raindrops and hold the surface. Shredded mulch knits together into a mat that stays put better than loose chips on the steepest parts.^[1]

Where a slope keeps losing soil, build low terraces. A short wall or a row of stones across the slope traps soil behind it and creates a flat planting step. With soft rock at about 26 inches, terraces stay shallow, so build them wide rather than deep. Fill the flat steps with Topsoil blended with Compost.^[1]

At the foot of a slope, a band of Riprap or a swale lined with River Rock slows water and catches soil before it reaches a patio or a drive. A Drain Rock trench behind any retaining wall lets water escape so pressure does not build up behind it.^[1],[2]

A drive built into sloped clay loam

Many drives here climb or cut across a slope. Strip the topsoil, shape the subgrade with a cross slope toward a ditch, and lay woven fabric on the silty clay loam. The fabric keeps the fine soil from working into the base as it swells and shrinks with the seasons.^[1]

Build compacted Road Base in thin lifts. Where the drive cuts into the slope, water seeping along the rock layer can come out at the cut face, so a Drain Rock trench along the uphill edge catches it before it softens the base. Crushed Concrete makes a firm, recycled alternative to Road Base.^[1]

For the top, Asphalt Millings hold well on a steep drive, since they bind together after rolling. 3/4" Crushed Stone or Driveway Gravel suits the flatter parking area. Set a few water bars on the steepest stretch to turn runoff aside.^[1]

Decomposed Granite or Walkway Gravel for garden paths

Garden paths on this ground need to survive dry months and the odd downpour. Decomposed Granite packs into a smooth, firm surface that suits the dry hills, while Walkway Gravel stays a little looser and lets more water through. On slow-draining silty clay loam, Decomposed Granite sheds water across its surface, so give it a slight side slope and a gravel edge to catch runoff.^[1],[2]

On a slope, Decomposed Granite can wash out where water runs down the path. Set steps or check dams of stone every so often, or choose Walkway Gravel for the steepest runs. Either path needs a compacted base of Road Base over fabric, so the clay below does not crack the surface as it moves.^[1]

Stone Dust Screenings make a good setting bed for flagstones laid along a sloped path, and they pack firmly between the stones.^[1]

Shredded mulch or Wood Chips on a dry hillside

A sloped, eroded yard with slow-draining soil needs mulch that stays where you put it. Shredded mulch and Wood Chips both shade the soil and slow evaporation, but they behave differently once the ground tilts. Brown Shredded Mulch, Black Shredded Mulch and Red Mulch are made of long, stringy fibers that tangle together as they settle, forming a mat that holds on a 15 to 30 percent slope even when a storm sends water across it.^[1]

Wood Chips are blocky and coarse. They last longer, breathe well and suit flat paths and the ground under trees, but on a steep slope they tend to slide downhill in the first hard rain. With only 16.8 inches of yearly precipitation at the Newhall station, mulch spends most of its life dry, and dry chips move even more easily under foot traffic or wind. Use shredded mulch on the slope itself and Wood Chips on the flat areas at the top and bottom.^[1],[2]

Over shallow soil above soft rock at about 26 inches, a few inches of mulch does more for plants than digging deeper ever could, since it keeps the thin root zone from drying out.^[1]

Homes in ZIP 93063 and the Caltrans spec

The Census counts 20,185 housing units in ZIP 93063. Detached single-family houses make up 69 percent of them, and owners live in 74 percent of the occupied homes.^[4]

Simi Valley as a whole holds 45,290 housing units, and 71 percent are detached houses. The median home dates from 1978 in the ZIP and 1980 across the city. A ZIP with mostly owner-occupied houses means many orders are for slope work, drive repairs and water-wise yard makeovers.^[4]

Many yards in the ZIP have had decades for slopes to slump, mulch to thin and drive edges to crumble. Before ordering, walk the property after a rain and mark where soil has moved, then plan stone and mulch for those spots first.^[4]

Caltrans specifies Class 2 Aggregate Base in Section 26-1.02B of its Standard Specifications (2026). That section covers the compacted stone layer under state highways.^[5]