This layer is a combination of Tier 1 and Tier 2 High Hazard Zones. They were merged together into this dataset to simplify use. The individual Tier 1 and Tier 2 datasets can be found in the Reference Layers feature dataset. Please see the metadata for HighHazardZones22_3_Tier1 and HighHazardZones25_1_Tier2 in the reference dataset for methods of creation of each layer. See below for a brief description of each layer.

Tier 1 High Hazard Zones: Tier 1 High Hazard Zones are where tree mortality directly coincides with critical infrastructure. They pose a threat to life and property. Tier 1 High Hazard Zones were last updated in 2020. CAL FIRE mapped Tier 1 High Hazard Zones by identifying assets to be protected as: communities, powerlines, roads, communication structures, and recreation facilities as well as miscellaneous other critical infrastructure. These assets to be protected were then buffered; communities were buffered by 1,000 feet and all other assets were buffered by 200 feet. Tree Mortality data was provided by the USDA Forest Service Forest Health Protection staff Aerial Detection Surveys from 2012-2015. Field review and revision was needed to refine and finalize HHZ areas. These zones were periodically updated to reflect new mortality or infrastructure assets at risk.

Tier 2 High Hazard Zones: Tier 2 High Hazard Zones represent areas for forest health restoration and fire planning. Tier 2 High Hazard Zones were updated in 2025. They were composed from the combination of ranked watersheds, FHSZ, and wildfires from 2012 forward (outlined below). Please see the Reference Layers for these input layers; their metadata contain further details about the methods by which they were created.

Watersheds: Areas with elevated tree mortality and high fire threat that are a hazard to public safety, community assets, and related infrastructure represent the primary focus of these zones. CAL FIRE mapped Tier 2 High Hazard Zones through a risk assessment model that scored watersheds based on amount of risk (hazard) and the amount of asset to be protected. This used the National Hydrography Dataset Watershed Boundaries (WBD) hydrologic unit code (HUC) 12 watersheds; these are the smallest consistently delineated watersheds in California and average around 24,000 acres in this model. The hazards utilized were: number of dead trees (from the USFS Aerial Detection Survey, 2015), acres of Tier 1 High Hazard Zones, and fire threat -- represented in the Sierra Nevada by WHRTYPE and fire return interval departure (USFS FRID, 2014) and in other areas of the state by CAL FIRE's Fire threat layer (FRAP, 2005). The assets to be protected were: amount of critical Infrastructure, represented by roads, communities, recreation facilities, communications); water related natural resources (represented statewide by acres of riparian and in the Sierra Nevada by acres of riparian and montane meadows); and amount of water infrastructure, represented by water conveyances, and water storage facilities. Each hazard and each asset was scored individually, and an overall composite score was achieved. The overall scores for hazard and assets were ranked and then also combined for an overall score. For more information on the datasets used and the scoring methodology, please contact thomas.crimmel@fire.ca.gov. These zones may be periodically updated to reflect new mortality or infrastructure assets at risk.

Wildfire Perimeters: As of 2020, Tier 2 also includes wildfire perimeters from 2012 to the present publish date. Starting with 2021, only fires over 100 acres are included.

Fire Hazard Severity Zone: As of 2020, Tier 2 also includes 'High' and 'Very High' Fire Hazard Severity Zones in forested areas.

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Emergency Declaration: On October 30, 2015 Governor Brown issued an emergency declaration requiring public agencies to identify areas of tree mortality that hold the greatest potential to result in wildfire and/or falling trees and threaten people and property in these areas. Once identified, these areas will be prioritized for removal of dead and dying trees that present a threat to public safety. https://www.caloes.ca.gov/wp-content/uploads/Legal-Affairs/Documents/Proclamations/20151030-Tree_Mortality_State_of_Emergency.pdf

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Update History:

October, 2025 Update: FHSZ was updated in the Tier 2 HHZ. The definition for the footprint of FHSZ to be concluded remained the same, but was clipped to FVEG22_1 WHR13NAME: Conifer Forest, Conifer Woodland, and Hardwood Forest. Fire perimeters greater than 100 acres from the 2022, 2023, and 2024 fire season were added. Middle Pine Valley Creek had 2 identical extents, Upper Pine Valley Creek had 2 identical extents, and Morena Reservoir-Cottonwood Creek had 2 slightly differing extents (they were almost identical, except that one had additional area). After consulting CA Waterboards public feature service for HUC12 extents, it was determined the larger of the two Morena Reservoir-Cottonwood Creek extents was the most up-to-date HUC12 extent. The three duplicate extents were removed. All inputs were dissolved into single feature polygons and then clipped to the extent of State25_1 before being merged together and dissolved. As a result, 994,596 acres were lost and 2,457,070 acres were gained from HighHazardZones22_3_Combined to HighHazardZones25_1_Combined. The final feature class was exploded for performance.

October, 2022 Update: Fire perimeters greater than 100 acres from the 2021 fire season were added. Fire perimeters from 2012-2020 were updated for new corrections. Several new fires were added.

May, 2021 Update: In accordance with the Emergency proclamation, Tier 1 HHZ is no longer being updated. FHSZ was directly added to the Tier 2 HHZ. The definition for the footprint of FHSZ to be included was updated with the following logic: FHSZ9 must be SRA_High, SRA_VH, LRA_High, LRA_VH, FRA_High, FRA_VH, and FVEG15_1 WHR13NAME must be Extent = FVEG WHR13 = Conifer Forest, Conifer Woodland and Hardwood Forest. Fire perimeters greater than 100 acres from 2020 were added. The FHSZ used in this update excludes Hardwood Woodlands, which were including in 2020.The attribute table was changed to only describe that this is Tier 2 HHZ. Please see the reference layers for the source of the polygons.

July, 2020 Update: Tier 1 HHZ has been updated using the USFS Region 5 Aerial Detection Survey (ADS) collected for the year of 2019. Damage Causing Agents (DCA) associated with drought-related mortality (i.e., insects and drought) were used to extract only the surveyed areas with drought related mortality.

October, 2020 Update: 5 locally designated watersheds were added.

April 2020 Update: High and very high Fire Hazard Severity Zones in State Responsibility Areas were added in 2020. It is a new addition to the Governor's Emergency proclamation High Hazard Zones that were initiated as a result of the 2015-2018 drought. The fire hazard zones provide specific designation for application of defensible space and building standards consistent with known mechanisms of fire risk to people, property, and natural resources. Four locally designated watersheds were added. Fire perimeters through 2019 were added.

April, 2019 Update: Tier 1 HHZ has been updated using the USFS Region 5 Aerial Detection Survey (ADS) collected for the of 2018. Damage Causing Agents (DCA) associated with drought-related mortality (i.e., insects and drought) were used to extract only the surveyed areas with drought related mortality. Tier 2 HHZ was updated using USFS Region 5 Aerial Detection Survey (ADS) of tree mortality collected during the year 2018. Three locally designated Tier 2 watersheds were also added. Wildfire perimeters from 2012 through 2018 were added in the update as well.

October, 2018 Update: Tier 2 HHZ were updated with 19 locally designated watersheds.

September, 2018 Update: An attribute was added to the HHZs describing the year they were designated.

March, 2018 Update: Tier 2 High Hazard Zones were updated in March of 2018 to incorporate the entire 2017 Aerial Detection Survey. Additionally, improved asset data was used for Placer county, including communities, local facilities, communications, and recreation. The USFS also updated their recreation assets in the 2018 update. An improved fire threat data layer was used for the entire state (FRAP, 2018).

February, 2018 Update: Tier 1 High Hazard Zones have been updated using USFS Aerial Detection Survey (ADS) collected for the year of 2017. Damage Causing Agents (DCA) attributable to drought (i.e., drought and insects) were used to extract only the surveyed areas with drought related mortality. New asset data was used for Placer county: communities, local facilities, recreation, utilities.

January, 2017 Update: The Tier 1 High Hazard Zones have been updated using the most current Aerial Detection Survey (ADS) released in November, 2016. Tier 2 High Hazard Zones were updated in January of 2017 to incorporate the full 2016 Aerial Detection Survey.

October, 2016 Update: Tier 2 High Hazard Zones were updated in October, 2016 with the May, 2016 Aerial Detection Survey of mortality flown by Region 5 USFS and with significantly improved critical infrastructure. Outreach to utilities during the spring of 2016 resulted in a much improved spatial data layer of utilities' critical infrastructure, one scoring component of Tier 2 High Hazard Zones.

August, 2016 Update: Tier 1 high hazard zones (HHZ) are the areas where tree mortality directly coincides with critical infrastructure. We originally delineated Tier 1 HHZ in December of 2015 using Aerial Detection Survey data from 2012 through October of 2015. In May of 2016 the USFS flew a new flight of the Aerial Detection Survey that was limited to lower elevations of the Sierra Nevada, Easter Cascades, and the Transverse ranges. This update of Tier 1 HHZ includes the new mortality flown in May of 2016. Additionally, it includes improved layers for critical infrastructure:

Utilities – utility companies from around the state contributed data to improve the location of their assets. CAL FIRE also contributed point locations for vital critical infrastructure.

Recreation – the USFS contributed data to improve the location of their recreation facilities.

Local Facilities – point locations for public schools, libraries, fire stations, and other local public buildings were added.

Water Conveyances – in addition to utilities contributing their critical water infrastructure, we added aqueducts, flumes, canals, and penstocks.

Roads – Mariposa county contributed an improved roads layer; the USFS provided USFS-designated roads for HHZ.