Siskiyou County

ADU Pass helps homeowners in Siskiyou County, California navigate the permit paperwork for building an accessory dwelling unit. We cover 21 cities and 22 ZIP codes in this county.

22 ZIP codes

21 Cities

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County ADU details

County ADU ordinance

Siskiyou County is California's fifth-largest county by area (~6,287 sq mi - bigger than Connecticut and Rhode Island combined) at the Oregon border, population ~44,000, with nine incorporated cities (Yreka, Mount Shasta, Weed, Dunsmuir, Tulelake, Etna, Fort Jones, Montague, Dorris) and substantial unincorporated territory including Happy Camp, Hornbrook, Klamath River, Hilt, Macdoel, McCloud, Lake Shastina, Greenview, Callahan, Sawyers Bar, Forks of Salmon, Cecilville, Seiad Valley, Scott Bar, Gazelle, Edgewood, and Grenada. The county seat is Yreka. The Mount Shasta volcano (14,179 ft, the iconic stratovolcano of the southern Cascades) anchors the county geographically. The county is bisected by the Klamath River (which flows from southern Oregon through Happy Camp and exits to Del Norte County) and contains the Salmon River drainage in the western Marble Mountain wilderness. The county Board of Supervisors administers ADUs in unincorporated areas under California Government Code Sec. 65852.2 and 65852.22. Politically Siskiyou is among the most state-resistant California counties (the State of Jefferson movement is concentrated here; the county has had multiple ordinance-conflict review cycles with HCD). The recent ADU permitting environment has been dominated by a sustained multi-year cycle of catastrophic fires: 2014 Beaver Fire, 2017 Eclipse Complex / Salmon-August Complex, 2020 Slater Fire (~157,000 acres into Oregon), 2021 Lava Fire (Mount Shasta vicinity), 2021 Antelope Fire, 2022 McKinney Fire (~60,000 acres west of Yreka, four killed) and Mill Fire (~3,930 acres in Weed, two killed, ~118 structures destroyed in town including substantial mobile-home and manufactured-housing footprint), and continuing fires through 2024-2025.

Code citations:

State-floor overlay: California state ADU preemption applies in full to unincorporated Siskiyou County. AB 1033 condo-conversion election: not adopted. AB 976 prohibits owner-occupancy mandates on detached ADUs. AB 2533 unpermitted-ADU amnesty applies. SB 9 urban lot-split provisions apply only within incorporated cities, not unincorporated parcels. HCD oversight applies to ordinance amendments per Sec. 65852.2(h); the county has had multiple HCD-flagged compliance review cycles given its political resistance to state housing preemption (the State of Jefferson movement is concentrated in this region). Owners should validate any local interpretation against the state-statute floor and assume the state-preemption baseline.

Adopting body: Siskiyou County Board of Supervisors

County permitting (unincorporated parcels)

Siskiyou County Community Development Department / Planning Division issues ADU permits for unincorporated parcels including Happy Camp, Hornbrook, Klamath River, Hilt, Macdoel, McCloud, Lake Shastina, Greenview, Callahan, Sawyers Bar, Forks of Salmon, Cecilville, Seiad Valley, Scott Bar, Gazelle, Edgewood, and Grenada. Practical permitting frictions: extensive CAL FIRE State Responsibility Area covering essentially the entire county outside the Shasta Valley / Scott Valley floor and the immediate municipal centers - the multi-year fire cycle (Slater 2020, McKinney 2022, Mill 2022, Antelope 2021, plus continuing fires) has reshaped WUI evacuation and Chapter 7A enforcement; the Mount Shasta volcanic-hazard zone (the USGS classifies Mt. Shasta as 'Very High Threat' active stratovolcano with extensive lahar / pyroclastic / debris-flow hazard mapping); Klamath National Forest (the bulk of the central and western county); Shasta-Trinity National Forest (southeast county); Klamath River corridor restoration zone (post-2024 dam removal); FEMA SFHA along the Klamath River, Shasta River, Scott River, Salmon River, McCloud River; the Cascade-Siskiyou National Monument (federal lands extending from Oregon into northeastern Siskiyou County); the Marble Mountain Wilderness and Trinity Alps Wilderness; tribal-trust lands of the Karuk Tribe (Happy Camp, Orleans), Quartz Valley Indian Reservation (Scott Valley), and Pit River Tribe (eastern county); high-elevation snow-load (Mount Shasta City at 3,500 ft, Macdoel at 4,259 ft, the upper Salmon River drainage above 5,000 ft); FEMA SFHA across the broad valley floors; and rural well-water / septic on essentially all unincorporated parcels.

DepartmentSiskiyou County Community Development Department, Planning Division

Address806 South Main Street, Yreka, CA 96097

Phone530-841-2100

Process overview: Standard ministerial 60-day review per Sec. 65852.2(b) for compliant ADU applications outside Very High FHSZ. Within Very High FHSZ (essentially the entire county outside the Shasta Valley / Scott Valley floor and the immediate municipal centers), Chapter 7A ignition-resistant construction, PRC 4291 defensible space, and CAL FIRE driveway/turnaround review apply. Multi-year fire-rebuild parcels (Slater, McKinney, Mill, Antelope, etc.) qualify for expedited replacement-permit pathways with comparable-utility base-year-value retention and disaster-relief reassessment. Mount Shasta volcanic-hazard-zone parcels carry advisory disclosure but no zoning prohibition. Klamath River corridor parcels (post-dam-removal restoration zone) are subject to active habitat-restoration overlay coordination. Tribal-trust parcels (Karuk Reservation, Quartz Valley Indian Reservation, Pit River trust lands) are governed by federal Indian law not county zoning. High-elevation snow-load engineering applies on most parcels. Septic-suitability evaluation by Environmental Health is required on essentially all unincorporated parcels.

Impact fees: SB 13 fee waivers apply to ADUs under 750 sqft (no impact fees). CAL FIRE driveway/defensible-space inspection fees apply on essentially all rural parcels. Septic permits required. School-district fees per Education Code Sec. 17620 on ADUs over 500 sqft (multiple small districts: Yreka Union ESD/HSD, Mount Shasta Union ESD/HSD, Weed Union ESD, Dunsmuir Joint USD, Tulelake Basin Joint USD, Etna USD, Happy Camp USD, plus several others). Insurance availability is acutely constrained post-Mill / McKinney / Slater Fire era - California FAIR Plan is frequently the only available wildfire-coverage option in the FHSZ corridors, and ADU construction-loan financing is materially affected.

County assessor

The Siskiyou County Assessor / Recorder maintains parcel-level assessment records for the entire county. ADU additions on unincorporated parcels are captured as improvements via shared permit data with Community Development. California Proposition 13 caps base-year valuation increases at 2 percent per year on the existing structure; new improvement value (the ADU) is added as a separate line item assessed at fair market value at completion. The county has substantial federal land (Klamath NF, Shasta-Trinity NF, Cascade-Siskiyou National Monument, BLM, Lava Beds National Monument in adjacent corner) which is exempt; private parcels constitute a smaller fraction of total county area but the bulk of assessed valuation. Williamson Act parcels exist in Shasta Valley / Scott Valley / Butte Valley (cattle/hay/ranching ag) carrying agricultural use-value assessment under Sec. 423 of the Revenue and Taxation Code. Recent fire-impacted parcels (Mill Fire 2022 in Weed, McKinney Fire 2022, Slater Fire 2020, etc.) qualified for Cal. Rev. & Tax. Code Sec. 170 calamity reassessment downward to reflect destruction, and Prop 50 / Prop 171 / Prop 19 disaster-relief base-year-value transfer for replacement structures of comparable utility.

NameSiskiyou County Assessor / Recorder

Address311 Fourth Street, Room 108, Yreka, CA 96097

Phone530-842-8036

Assessment policy: ADU improvement value is added on the next regular revaluation cycle following completion. Per Prop 13, the ADU's value is taxed at 1 percent of fair market value at completion (plus voter-approved local rates), while the existing structure remains at its base-year value plus the 2 percent annual cap. Conversion ADUs (within existing structure) typically generate smaller incremental assessments than detached new construction. Multi-year fire-impacted rebuild parcels: replacement structure of comparable utility carries the pre-fire base-year value; an ADU added during rebuild that exceeds comparable-utility floor area is assessed at fair-market new-construction value for the excess.

County overlays (8)

Siskiyou County overlays of consequence: CAL FIRE State Responsibility Area Very High FHSZ across essentially the entire county outside the Shasta / Scott / Butte Valley floors and immediate municipal centers; multi-year fire-rebuild zones (Slater 2020, Antelope 2021, Lava 2021, McKinney 2022, Mill 2022, plus continuing fires); Mount Shasta volcanic-hazard zone (USGS Cascade Volcano Observatory; Mt. Shasta is rated 'Very High Threat' with extensive lahar / pyroclastic / debris-flow hazard mapping); Klamath National Forest (~1.7 million acres) and Shasta-Trinity National Forest (the second-largest NF in California, southeast county portion); Marble Mountain Wilderness and Trinity Alps Wilderness; Cascade-Siskiyou National Monument (extending from southern Oregon into northeastern Siskiyou County); Lava Beds National Monument (NPS, in adjacent Modoc / Siskiyou corner); Klamath River wild and scenic corridor with post-2024 dam-removal restoration zone (Iron Gate Reservoir drawdown and channel restoration); FEMA SFHA along the Klamath River, Shasta River, Scott River, Salmon River, McCloud River; high-elevation snow-load overlays; Karuk Tribe Reservation (Happy Camp / Orleans area), Quartz Valley Indian Reservation (Scott Valley), Pit River Tribe trust lands, and Shasta Tribe ancestral-territory consultation (AB 52 / SB 18); Williamson Act ag-preserves in the broad valley floors.

Known county issues (5)

policy-review — Political-friction risk: Siskiyou County is among the most state-resistant California counties (the State of Jefferson movement is concentrated here). Local ordinance amendments have had multiple HCD compliance review cycles. Owners should validate the latest local ordinance against the state floor and assume the state-preemption baseline rather than rely on local interpretations that may be in friction with HCD.
other — Multi-year fire-rebuild concentration: Slater (2020), Antelope (2021), Lava (2021), McKinney (2022), Mill (2022 in Weed), and continuing fires through 2024-2025 have concentrated rebuild activity across multiple footprints concurrently. The Mill Fire in Weed alone destroyed ~118 structures in town with substantial manufactured-housing displacement. Insurance availability is acutely constrained; CA FAIR Plan is frequently the only wildfire-coverage option.
other — Mount Shasta volcanic hazard: Mt. Shasta is rated 'Very High Threat' by the USGS. While ADU permitting is not zoning-prohibited in the volcanic-hazard zone, lahar / debris-flow corridors down Whitney / Mud / Ash Creek and the upper McCloud River drainage carry advisory disclosure. Structural design on alluvial-fan parcels should accommodate seasonal debris-flow risk.
other — Klamath River corridor restoration: post-2024 dam removal has reshaped the Iron Gate / Hornbrook / Klamath River corridor. Active habitat-restoration overlays and revised FEMA flood-zone mapping apply. Owners should validate the most current zoning, riparian-buffer, and flood-zone determinations at permit application.
other — Tribal-trust complexity: multiple federally-recognized tribes (Karuk, Quartz Valley IRA, Pit River) hold trust holdings; the non-federally-recognized Shasta Indian Nation asserts ancestral-territory interest across the bulk of the county. CEQA-triggered ADU projects in culturally-significant areas trigger AB 52 / SB 18 consultation; tribal-trust parcels are entirely outside county zoning jurisdiction.

California state — ADU law and programs

State ADU law

California has the most aggressive statewide ADU preemption regime in the US, built from ~15 bills passed 2019-2025 and enforced by the Department of Housing and Community Development (HCD). The 2026 HCD ADU Handbook addendum (in effect with the 2025 Title 24 code cycle) is the operative state-level reference. The regime does four things at once: (1) preempts local zoning that would ban or unreasonably restrict ADUs; (2) imposes by-right ministerial approval with short statutory deadlines; (3) caps fees and utility-connection charges; and (4) empowers HCD to void non-compliant local ordinances.

State HOA preemption

California has the strongest statewide HOA-preemption regime in the US for accessory dwelling units, built from two bills: AB 670 (2019) voided ADU-prohibiting covenants on single-family residential lots, and AB 3182 (2020) extended and codified the preemption into the Davis-Stirling Common Interest Development Act (Civil Code §§ 4740 / 4741). The combination prohibits common-interest communities from banning ADUs, restricting rentals below 25% of separate interests, or treating ADUs as separate HOA interests. Limits remain: HOAs retain authority over reasonable design standards and statutory height limits, and the 2026 Carlsbad case (CalMatters coverage) established that an HOA's documented design-standards regime can effectively delay or constrain ADU approval short of outright prohibition.

State financing programs

California's flagship state-level ADU financing program — the CalHFA ADU Grant Program — is paused and has not been refunded since the original $100 million allocation was fully deployed 2023-12-28. The program provided up to $40,000 per qualifying homeowner for pre-construction and non-recurring closing costs and financed approximately 2,500 ADUs in two rounds. As of 2026-04, no new funding round has been announced in the state budget. CalHFA continues to publish anti-scam warnings because bad actors actively solicit homeowners claiming access to grant funds that no longer exist. State-level financing activity has shifted to local pilot programs (San Francisco, San Jose, Los Angeles, San Diego) and private financing products (Fannie Mae ADU mortgage, HELOC, construction-to-permanent).

CalHFA ADU Grant Program
HCD ADU Funding index

State housing programs

California's state-level ADU programs are concentrated at HCD (technical guidance, ordinance review, enforcement) and the paused CalHFA grant pipeline (covered under stateFinancing). The state does not operate a central pre-approved ADU plan library — instead, AB 1332 (2024) created a preemption framework for local pre-approved plans with a 30-day ministerial-approval deadline, and major cities (Los Angeles, San Diego, San Jose, Sacramento, Berkeley) have rolled out their own plan catalogs. The California YIMBY coalition and other housing-policy organizations play an influential role in bill drafting; they are not state agencies but effectively drive much of the ADU legislative agenda. The Title 24 code cycle (now 2025, in effect for 2026 permits) is the authoritative building-code baseline.

Federal (United States) — ADU-relevant rules and programs

Federal ADU law

The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.

Federal financing programs

Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.

Federal tax credits

There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.

Federal housing programs

HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.