Soil Conditions in Pasadena
Los Angeles County's geology is as varied as its neighborhoods. Here's what we typically find.
San Gabriel Mountains Alluvial Fan
Pasadena is built on a large alluvial fan emanating from the San Gabriel Mountains. The alluvium consists of poorly sorted gravel, cobble, sand, and silt deposits that are generally dense to very dense at depth. Upper fan deposits near the mountains are coarser and more bouldery, which can challenge drilling operations.
Collapsible Soils in Upper Fan Areas
The upper alluvial fan deposits in northern Pasadena and near the Arroyo Seco can exhibit collapsible soil behavior — settlement triggered by wetting of loose, dry granular soils under load. Identification of collapsible soils requires specific laboratory testing and often leads to over-excavation and recompaction recommendations.
Raymond Fault Zone
The Raymond fault crosses through southern Pasadena and is an Alquist-Priolo Earthquake Fault Zone. Properties near the fault trace require a fault rupture hazard investigation before building permits are issued. The fault also defines a boundary between the deeper alluvial basin to the south and the shallower fan deposits to the north.
Hillside Overlay and Debris Flow
The northern neighborhoods of Pasadena adjoin the San Gabriel Mountains and are subject to debris flow and rockfall hazards, especially following wildfires. The city's hillside overlay district imposes additional geological investigation requirements and limits on grading and development intensity.
What We Do in Pasadena
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/WQMP compliance 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 Pasadena
Single-Family Home
New custom homes in Pasadena range from flatland infill near South Pasadena to hillside estates in the San Rafael and Linda Vista areas. Each setting presents distinct geotechnical challenges.
ADU / Accessory Dwelling Unit
Pasadena has actively promoted ADU development. Soils reports are required for most new ADUs and are especially important on properties with collapsible soils or in seismic hazard zones.
Historic Property Renovation
Pasadena's extensive historic districts include properties requiring seismic retrofit and foundation upgrades. Geotechnical investigation informs underpinning, foundation bolting, and structural rehabilitation design.
Commercial and Institutional
Projects along Colorado Boulevard and in the Civic Center area require geotechnical investigation for new buildings and underground parking structures, often encountering shallow groundwater and dense alluvium.
Hillside Retaining Walls
Engineered retaining walls are common in Pasadena's hillside neighborhoods for driveway access, building pad creation, and slope stabilization following erosion or shallow failures.
Working With City of Pasadena Building & Safety Division
Pasadena Building & Safety requires geotechnical investigations for new construction, grading permits, and projects within the hillside overlay district or mapped hazard zones. The city reviews reports in-house and may request peer review for complex hillside projects. Building permits are processed through the Pasadena Permit Center.
What Makes This Jurisdiction Distinct
Hillside Overlay District imposes grading limits, geology report requirements, and floor area restrictions on steep slopes
Raymond fault zone investigation required for properties within the Alquist-Priolo zone
Collapsible soil evaluation recommended for properties on upper alluvial fan deposits in northern Pasadena
Debris flow and rockfall hazard evaluation required for properties near mountain fronts
Historic district review may apply to grading and construction in designated historic neighborhoods
Submit geotechnical reports to the Pasadena Permit Center with the building or grading permit application. Hillside projects benefit from a pre-application conference with Building & Safety to clarify investigation scope before fieldwork begins.
Common Questions — Pasadena
Building in Pasadena?
Tell us about your project and we'll send you a fixed-fee proposal — typically within one business day.