Inland Empire Soil Types: A Landscaping Guide

The Inland Empire has seven major soil series. Ramona sandy loam dominates Riverside and Corona terraces. Hanford sandy loam lines the Santa Ana River floodplain from Ontario to Norco. Greenfield sandy loam covers Temecula and Murrieta wine country. Fallbrook sandy clay loam sits on foothill areas in Highland and Banning. Vista series decomposed granite soils appear on granitic slopes throughout the region. Arlington clay loam creates drainage problems in low-lying Riverside and Ontario areas. Bonsall series expansive clay, the most challenging IE soil, causes shrink-swell damage in Menifee, Temecula, and parts of San Bernardino.

Three signs: wide cracks in your yard during dry months (sometimes 1-2 inches wide and several feet deep), sticky mud that clings to shoes after rain, and doors or windows in your home that stick seasonally as the foundation shifts. You can do a simple jar test, put soil in a mason jar with water, shake it, and let it settle for 24 hours. If the top layer (clay) makes up more than 30% of the total, you have significant clay content. For definitive results, send a sample to a soil lab for a Proctor compaction test and Atterberg limits analysis, which will give you the Plasticity Index (PI), anything over 20 is highly expansive.

Yes, but you need a deeper base than standard ICPI specs call for on stable soil. On Bonsall or Arlington clay, excavate 10-12 inches deep instead of the standard 6-8 inches. Install 6-8 inches of Class II road base compacted in 2-inch lifts to 95% Proctor density, then 1 inch of bedding sand. The thicker base acts as a buffer against shrink-swell movement. We also recommend a geotextile fabric between the native clay and the base material to prevent clay migration. French drains along the perimeter keep water from saturating the clay beneath the paver field.

It depends on your specific soil type. In sandy Ramona and Hanford soils (Riverside, Corona, Ontario), most Mediterranean and drought-tolerant plants thrive, Bougainvillea, Citrus, Lavender, Rosemary, and California Pepper trees. In clay-heavy Bonsall and Arlington soils (Menifee, parts of San Bernardino), choose plants that tolerate wet feet in winter and drought in summer, California Sycamore, Toyon, Western Redbud, and native bunch grasses. In DG Vista soils (foothill areas), desert-adapted species perform best, Desert Willow, Manzanita, Ceanothus, and Agave. The IE sits in USDA Zones 9b-10a, which is warmer than the High Desert and supports a wider range of subtropical species.

On expansive clay (Bonsall or Arlington series), the footing should extend at least 24 inches below grade, deeper than the 18-inch minimum on stable soil. The footing width should be twice the wall thickness. Use a concrete footing with #4 rebar on 16-inch centers rather than a compacted gravel base. The concrete footing resists the lateral pressure that expansive clay exerts when wet. Most IE jurisdictions require a building permit for walls over 3-4 feet, and the geotechnical report will specify the exact footing depth based on the Plasticity Index of your specific soil.

Sandy loam soils like Ramona and Hanford (found in Riverside, Corona, Norco, Ontario) are excellent for warm-season turf grasses like Bermuda and St. Augustine. They drain well and warm up quickly in spring. Clay soils like Bonsall and Arlington are more difficult, they stay waterlogged in winter (causing fungal diseases) and crack in summer (tearing root systems). On clay, consider artificial turf or drought-tolerant groundcovers instead. Regardless of soil type, the IE’s USDA Zone 9b-10a climate and 12-15 inches of annual rainfall mean you will need irrigation for any natural lawn, expect to water 3-4 days per week in summer.

The UC Riverside Cooperative Extension offers soil testing services and interpretation for homeowners. The Inland Empire Resource Conservation District (IERCD) runs periodic free soil testing programs. For construction projects requiring geotechnical analysis (retaining walls, foundations, large hardscape installations), hire a licensed geotechnical engineer who will perform Proctor compaction tests, Atterberg limits, and sieve analysis. Commercial labs like Alluvial Soil Lab also serve the IE region. A basic pH and nutrient test costs $25-50; a full geotechnical report runs $1,500-3,000.

Expansive clay soil is the primary cause. Bonsall and Arlington series soils swell when wet and shrink when dry, creating cyclical ground movement that standard 4-inch residential slabs cannot withstand. In neighborhoods built on these soils, common in Menifee, parts of Temecula, south San Bernardino, and low-lying Ontario, you will see cracked driveways, buckled sidewalks, and foundation issues. The fix for new concrete is a thicker slab (5-6 inches), #4 rebar on 12-inch centers instead of wire mesh, control joints every 8 feet, and a 4-6 inch compacted gravel sub-base to buffer the clay movement. Proper grading to direct water away from the slab is equally important.

Only when the clay is sodium-affected, which a soil test identifies (look for an SAR above 13). Most Inland Empire clay is expansive montmorillonite, not sodic, so bagged gypsum does very little. Composted organic matter worked into the top 12 inches, drainage that routes water away from the clay, and clay-tolerant plants outperform gypsum in almost every IE yard.

For heavy clay, tall fescue blends tolerate the slow drainage better than most warm-season grasses. For sandy, fast-draining soil in full sun, hybrid Bermuda performs well on less water. Where the soil fights every option, artificial turf sidesteps soil quality entirely and stays green through both extremes, which is why turf conversions are common on the toughest IE lots.