Geologic & Geotechnical FAQs

County staff have received many questions related to the Atkins Study and CZU Rebuild Directive applicability and these affect the overall rebuild permit process. A list of frequently asked questions and answers is provided below.

Atkins and Debris Flow FAQs


The Atkins Study consists of a hydraulic (water mechanics) model that shows where muddy water will flow in an intense storm. Debris flows may include higher amounts of soil, trees, rocks and debris, and will generally inundate the same locations as muddy water based on the topography of the affected drainage basins. While debris flow material differs from water in the weight of the material and flow mechanics, the inundation areas, velocities and flow depths yielded by the hydraulic model are reasonable estimates for a debris flow with a lower sediment content. Your engineer will likely include some safety factor in their recommendations to account to debris flows with higher sediment content, which may be thicker.


The Atkins Study debris flow map (in addition to other pertinent maps) is used by geologic staff to determine whether CZU rebuild home sites are subject to potential debris flow hazards during the Geologic Hazard Pre- clearance review. Building sites that fall within the areas labeled “Primary Debris Flow Path” and /or “Uncertain Debris Flow Path” are considered subject to debris flow hazards. Please note that if your building site falls OUTSIDE the Primary and /or Uncertain Debris Flow paths the building site may still be prone to debris flow hazards (see FAQ 10 below).

Areas shown within the “Primary Debris Flow Path” boundary have a higher likelihood of being inundated by a debris flow, and may experience higher velocities and more destructive forces during a debris flow event. Depth and velocity model data is available within the Primary Debris Flow Path areas.

"Uncertain Debris Flow Path" boundaries delineate areas where the debris flow could jump out of the “Primary Debris Flow Path” due to a change in grade, channel blockage or other factors. These areas are at elevated risk of inundation by debris flow, but due to uncertainties in the direction flow will take, they are at relatively lower risk than those in the “Primary Debris Flow Path” areas. Due to the many variables that influence debris flow path, the Atkins Study model output does not include depth or velocity values for the "Uncertain Debris Flow Path" areas.


Your geotechnical engineer will use their professional skills and judgement as a state-licensed engineer to determine how to consider the hazard in the structure and/or site design. Once plans are completed, your geotechnical engineer will need to produce a “plan check letter” stating that the geotechnical recommendations have been properly incorporated into the plans. Recovery Permit Center (RPC) plan check staff will collect that letter and help to ensure that the recommendations of the geotechnical report are reflected in the home design and calculations.

Atkins Study data is just one source of information that will be used by the project geotechnical engineer to determine how the rebuilt home design will address the potential for debris flow. In some cases the geotechnical engineer may request additional information from a geologist to assist with their recommendations; if the property owner has “opted out” of SCCC 16.10, this additional geologic information will not be peer reviewed by County staff.

County staff have met with local geotechnical engineers on both an individual and group basis to discuss how they may utilize the Atkins Study data to satisfy the requirements of the California Building Code, and will continue to assist however possible to facilitate use of this valuable data by industry professionals.

If you plan to rebuild in conformance with 16.10 and not “opt out” by using the CZU rebuilding directive, your geotechnical engineer may provide a more expanded analysis, and will make specific recommendations for mitigation measures that can lower the risk to the rebuilt home.

Technical professionals can download the Atkins Study shapefiles and raster data via the County Geographic Information Services (GIS) open data website:


Atkins Study debris flow zone maps are hosted on the County GIS web application as the “Atkins Study” layer under the "Hazards and Geophysical" tab.

The Atkins Study .PDF maps are at a 1:500 scale and provide building footprints that are based on optical tracing of aerial photographs with a +/- 10 foot accuracy. Not all buildings shown are dwellings, and only buildings visible from the air are shown. It should be noted that parcel layers in the CZU burn area are highly inaccurate (up to +/- 300 feet in some locations), so the most reliable way to determine the location of your home site relative to the reported debris flow hazard areas is by zooming to your homesite’s geographic coordinates via the “Measure Lat/Long” tab at the top of the County GIS web screen; your design professional may be able to assist with this. You can obtain the geographic coordinates for your site by using a gps receiver or the gps function in your phone.


If your building site touches the debris flow hazard area, your project is within an area subject to potential debris flow hazards and requires further evaluation.


No, if your site was shown within the Atkins primary or uncertain debris flow hazard areas and is moved outside the Atkins Study debris flow hazard zones, no further mitigation for debris flow hazards is required to comply with County Code Chapter 16.10. The location of your building site relative to the Atkins Study debris flow hazard area will be confirmed during the Geologic Hazard Clearance review of your build site. Please note that if your building site falls OUTSIDE the Atkins study "primary" and/or "uncertain" Debris Flow paths the building site may still be prone to debris flow hazards (see FAQ 8 below).


NO! As a tool for fire survivors who wish to rebuild, the Atkins Study focused on larger drainage basins that have affected parcels with destroyed structures. Consequently, basins without fire damaged structures were not included in the Atkins Study detailed mapping areas. The best sources of data for determining whether you are at heightened risk for winter debris flows and/or evacuations are the debris flow hazard maps, which are available as layers on the County GIS web application titled "CZU Potential Debris Flow Hazard Areas" layer under the "Hazards and Geophysical" tab.

Are there other Important things to know?

Is it key that your geotechnical engineer, civil/structural engineer and architect or design professionals all work together to ensure the project geotechnical report recommendations are properly and consistently reflected in the plans and calculations. Your geotechnical engineer will be asked to provide a plan review letter stating that this is the case. You should ensure that the geotechnical engineer is prepared to provide this letter.

After building permit issuance, the geotechnical engineer must stay involved with the project to ensure it is constructed in conformance with the geotechnical report recommendations. Communication among your team throughout construction is key to success!


Not necessarily. Some drainages outside the Atkins detailed study area are still considered subject to debris flow hazard and were included in the “CZU Potential Debris Flow Hazards layer prepared by the County. Building sites in these areas will also need to consider debris flow hqzard. The location of the building site relative to designated debris flow hazard areas will be confirmed by County geologic staff during the Geologic Hazards Clearance review.


Rebuild Directive FAQs


If you have already received an issued Geologic Hazard Clearance no further action is required on your part.


Geologic reports can take months to schedule and complete testing and can cost thousands of dollars. Those choosing to proceed under the CZU Rebuild Directive are relieved of the County requirement for a geologic report and receive Geologic Hazard Clearance to apply for a building permit without County review of technical reports.

Please be aware that your geotechnical (soils) engineer, may require additional geologic information, even if the County doesn’t require it. It’s imperative that you meet with your geotechnical (soils) engineer to discuss geologic issues.


The CZU Rebuild Directive only applies to applications submitted by the property owner as of August 16, 2020. Those purchasing a property that have received a Geologic Hazard Clearance result indicating further geologic evaluation is required will need to submit Geologic and/or Geotechnical (soils) reports for County review prior to issuance of a Geologic Hazard Clearance to submit a building permit application. See comments on the geologic pre-clearance for more information.


County staff have modeled the “Notice of Geologic Hazards” after a similar recorded document required for non-CZU rebuild proposals in geologically hazardous areas of the County for the past 25 years. During that time, the County has not been made aware of any negative impacts to property values or insurability tied to the recorded document. County staff have spoken with banking and insurance industry professionals and confirmed that the document would not pose an issue for those entities.

  1. Apply for a Geologic Hazard Pre-Clearance if you have not done so already. The clearance will let you know whether the County requires further geologic evaluation for your rebuild site, and whether the project is eligible for processing under the CZU Rebuild Directive. Please reach out to the RPC for information on submitting the pre-clearance applications and use of the Rebuild Directive.

Once the pre-clearance has been completed, please complete the following steps:

  1. If your project is eligible and you choose to process your permit under the CZU Rebuild Directive, submit a signed copy of the CZU Rebuild Directive Acknowledgement Form to the RPC.
  2. Prior to building permit application issuance the property owner must sign, notarize and record a “Notice of Geologic Hazards” on the property title. The “Notice of Geologic Hazards” document will be provided to the applicant by County Geologic staff with the final pre-clearance approval letter.


For rebuilders who are within the Atkins Debris Flow area and whose Geologic Hazard pre-clearance result noted debris flow as the only hazard of concern, the Atkins Study results satisfies the County Code Chapter 16.10 requirement for a geologic report. In these cases, a Geotechnical (soils) Report is required. The report must meet building code requirements and must provide mitigation recommendations to address the debris flow hazard.

Those choosing to proceed under the CZU Rebuild Directive can obtain their Geologic Hazard Clearance must submit their geotechnical (soils) report with their building permit application.

In contrast, rebuilders that choose to rebuild without use of the CZU Rebuild Directive are required to submit the geotechnical (soils) report for acceptance prior to obtaining a Geologic Hazard Clearance. The project engineer must sign and stamp a Geotechnical Engineer of Record Statement, which states that they have reviewed County guidance for debris flow hazard assessment and mitigation and have provided debris flow mitigation recommendations. Refer to more detailed information here.

In addition, prior to building permit application issuance the property owner must sign, notarize and record a “Notice of Geologic Hazards” on the property title. The “Notice of Geologic Hazards” document will be provided to the applicant by County Geologic staff with the final pre-clearance approval letter.


No. Those choosing the CZU Rebuild Directive will submit their geotechnical (soils) report as part of their supplemental documents, and plans will be reviewed to ensure the design recommendations in the soils report are reflected in the design and calculations. The soils report must include the geologic hazards noted in the Geologic Hazards Clearance, but the adequacy of the mitigation recommendations is determined by the Geotechnical Engineer of Record that prepared the report.

Regardless of permit processing path, a plan review form (PLG300) will be required to be submitted with the building permit application, in which the Geotechnical (soils) Engineer confirms that the project plans were prepared in conformance with the Geotechnical (soils) Report.


No. While the County may not require a Geologic Report to process applications submitted under the CZU Rebuild Directive, geotechnical engineers may determine during the course of their independent site investigation that further geologic information is required in order for them to produce mitigation recommendations.


Yes. If you meet eligibility requirements for the CZU Rebuild Directive you can choose that processing path at any time by submitting a signed CZU Rebuild Directive Acknowledgement Form with your building permit application materials.

Please note that the fee for County peer review of technical reports is $1,000 and is non-refundable after review comments are issued by the County reviewer.