Soil Conditions in El Cajon
San Diego's geology varies dramatically from neighborhood to neighborhood. Here's what we see most often.
Stadium Conglomerate
El Cajon sits in a valley surrounded by hills of Stadium Conglomerate, a cemented cobble-bearing formation. This material has high bearing capacity when intact but can be extremely difficult to excavate. Projects on hillsides encounter this formation frequently.
Alluvial Valley Fill
The El Cajon Valley floor contains alluvial deposits from the surrounding hills — silty sands, sandy clays, and gravelly soils with variable density. Expansion potential varies significantly from site to site, requiring testing on each project.
Decomposed Granite
Granitic bedrock and its weathered product, decomposed granite (DG), underlie parts of eastern El Cajon. DG drains well but can be collapsible when loose, and excavation conditions vary from easily rippable to requiring rock hammering.
What We Do in El Cajon
Soils Reports
Geotechnical investigation and foundation recommendations for building permits.
Learn more →Grading Plans
Precise and rough grading design with drainage and earthwork calculations.
Learn more →Compaction Testing
Field density testing and fill certification for construction.
Learn more →Stormwater / LID / WQMP
LID compliance, WQMP preparation, and BMP design.
Learn more →Hydrology Reports
Drainage analysis and flood risk assessment.
Learn more →Subsurface Exploration
Drilling, CPT, and test pit programs.
Learn more →Erosion Control Plans
SWPPP and erosion control for grading permits.
Learn more →Street Improvements
Frontage, curb, gutter, and sidewalk design.
Learn more →Utility Plans
Water, sewer, and storm drain design and coordination.
Learn more →Project Coordination
One point of contact managing structural, MEP, surveying, and specialty consultants.
Learn more →We also coordinate with your structural engineer, architect, MEP consultants, and other project team members to ensure our deliverables integrate with the overall design — one point of contact for your geotechnical and civil engineering scope.
What People Build in El Cajon
Single-Family Home
New home construction in El Cajon's valley and hillside neighborhoods, each presenting different soil conditions and engineering challenges.
ADU / Accessory Dwelling Unit
ADU construction on existing residential lots. Soils reports are required for new detached structures.
Retaining Walls
Hillside properties often require engineered retaining walls with proper drainage and lateral earth pressure design.
Commercial Renovation
Downtown El Cajon commercial redevelopment projects on alluvial valley soils.
Working With City of El Cajon Building Division
El Cajon requires geotechnical investigations for new construction and significant grading. The Building Division reviews reports as part of plan check. Hillside properties may require additional slope stability analysis.
What Makes This Jurisdiction Distinct
Hillside development overlay requires slope stability analysis for sites with slopes over 25%
Grading permits required for earthwork over 50 cubic yards or cuts/fills deeper than 3 feet
Stadium Conglomerate excavation often requires pre-construction site assessment for contractor planning
Stormwater compliance required per San Diego Regional MS4 permit
Submit to El Cajon Building Division at 200 Civic Center Way. Plan check is typically 3-4 weeks for residential.
Common Questions — El Cajon
Building in El Cajon?
Tell us about your project and we'll send you a fixed-fee proposal — typically within one business day.