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Geological Inspection

Vasquez Rocks Park in Agua Dulce

What is a GEO?

“Geo” is short for Geological Inspection. Geo Inspections are done by Geologists who evaluates the risk, from a geological standpoint, of buying a home in escrow. Geologists rate risk on a scale of low, medium/average, or high.

The steeper the slope- the greater the force of Gravity.

I always recommend to get a Geological Inspection for hillside properties. Hillside properties have gravity working against them, so it is important to ensure that the geological conditions of the lot are stable. A house is only as good as the foundation it is built on, and a foundation is only as good as the bedrock it rests on top of.

If the property has or has had a geological problem in the past like a Landslide, Slope Failure, Erosion, Creep, Collapsed Retaining wall, etc, these are expensive and can cost in the $100,000’s of dollars and could make the property unmarketable!

A GEO inspection protects you from buying a property with a known or observable Geological defect. 

GEO inspections have two parts:

(1) Site Visit: the geologist and visual inspection of the property.

(2) Research: the geologist reviews city records and reports including building permits, previous soils tests, grading reports, historic landslide information, proximity to active faults, and geological bedrock survey maps.

At the end of the inspection, the geologist will write a report that summarizes all of their findings.

Geological Inspections do not include testing. The purpose of a GEO is to satisfy the buyer’s due diligence during escrow and not to be used for obtaining approval of building plans. No testing keeps cost down- a GEO inspection is 1/3 to 1/5 of the cost of a Soils test.

How do I tell if my property is Hillside?

You can usually tell just by looking around. Hillside properties are in the mountains, so if you see any big hills or slopes, you are probably in a hillside area.

Hillside Areas Are Shaded

Los Angeles has a special zoning designation for Hillside properties. You can look up the zoning information on the city’s zoning website ZIMAS. The main characteristic that defines a hillside property is slope.

The definition of a Slope (LABC 7003)

SLOPE. An inclined ground surface the inclination of which is expressed as a ratio of horizontal distance to vertical distance. Slope greater than 10% shall be considered as a sloping surface.

What does a GEO inspection Cover?

The GEO covers several different topics that relate to the hillside: Drainage, Grading, Soil/Bedrock, Seismicity, Landcaping, and Foundation.


Controlling stormwater runoff is the most important thing to keep your hill safe. Good drainage also protects your foundation from deterioration. Los Angeles doesn’t get much rain, but the occasional heavy rainstorm can dump 5 to 10 inches quickly, which can lead to landslides and slope failures (especially after wildfires) if your property doesn’t have proper drainage.

Soil naturally absorbs water, so having some open areas of permeable surfaces on the lot that can absorb runoff and not all concrete pavement helps drainage. For excess water, the best place to drain is in the streets that are connected to the city’s stormwater system and empty into the ocean.

Sometimes on hillside lots, especially downslope lots from the street, it is not practical to drain to the street which would require pumping the water uphill. If you can’t connect to the stormwater system, then an onsite drainage system such as a dispersion wall, sump pump, swale, or cross-lot drainage easement can be built to direct the runoff to an approved location.

It is illegal to send your stormwater runoff into the sewer system, which is a different system altogether. If everybody drained their stormwater into the sewers, the sewers would overflow! Storm surges can move 10 billion gallons of water in just 1 day. In addition, it is very costly to treat sewer water at waster water treatment plants, whereas stormwater is not treated.


Grading is shaping the land by moving topsoil. Hillsides are sloped. You need a flat pad to build on. Grading sculpts the land to prepare it for building.

Grading Diagram

When you remove soil- this is called a “cut”. When you add soil- that is called a “fill”. Depending on the soil composition, sometimes you can use your cut from the same site as fill, which can save a lot of money in hauling and materials costs.

Fill is where you sometimes run into trouble. Prior to the enactment of the Grading Code in 1963, fill was not generally well compacted, which lead to an excessive amount of settlement, landslides, and erosion. If your Geological inspection reveals that the lot has fill prior to 1963- be extra careful.

Compaction Diagram

I’d also like to mention that fill should be free of large rocks or boulders and debris- Soil holds weight much better when there are no large obstructions to the compaction. I know in some neighborhoods in the hills, when the original grading was done, the developers did the grading hastily left a bunch of large rocks mixed in that has led to geological problems later on.

Just like you have setbacks for the front yard, backyard, and side yards, of your house- you have required setbacks from the hillside of your lot. There are two reasons for the hill setback- 1) the more flat land between the foundation and slope, the more bearing capacity of the soil and 2) if there is a rockfall or a mudslide you house has a better chance of being a safe distance away from it. The amount of the hill setback varies. 

Soil/Bedrock Conditions

Geologists study rocks and dirt. When you start learning about Geology, it’s actually pretty cool! The first rocks on Earth formed about 4 billion years ago. Since that time the surface of the Earth has changed quite dramatically- and it’s still changing. Los Angeles is moving towards San Fransisco along the San Andreas Fault at the rate of a few inches each year which means that in about 15 million years these two cities will be connected!  

Sand- Water drains quickly through sand.

Silt/Loam- Just the right amount of sand and clay and organic materials, basically dirt. 

Clay- Clay absorbs water, and expands and contracts. Too much clay in the soil can create expansive soils. 


There are 4 main types of Bedrock in Los Angeles Area:
and estimate how far below the surface the bedrock is. The closer to the surface the bedrock is, the better.
Bedrock is what you anchor your foundation to and what gives it strength. Bedrock 5 – 10 below the surface is close to the surface, 20-30 feet below the surface is average, and 40 feet or more means the bedrock is very far from the surface and it can be very costly to anchor the foundation with caissons. 
Types of Bedrock:


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