Siskiyou County — Overlay Districts

Last reviewed: July 6, 2026

Overview

In unincorporated Siskiyou County, “overlay” or “combining” districts layer special rules on top of the base zoning shown on the parcel. Overlays are established under Title 10 (Planning and Zoning) and include, among others, the Airport Environs (AE) Combining District, Floodplain (F) Combining District, Fault-Rupture Zone (FRZ) Overlay District, Mobile Home (M‑H) Combining District, and Hemp (H) Combining District. The County’s zoning plan explicitly recognizes combining and special hazard districts alongside the residential, commercial, industrial, and agricultural districts in the unincorporated areas (§ 10-6.202 ).

Most important rule: when an overlay conflicts with base zoning, the more restrictive overlay standard governs (§ 10-6.5402; § 10-6.6003 ).

Use this page together with the County’s zoning, land use, and cross-cutting development standards. If a project in an overlay adds a building or site work, also check parking and whether any design review applies. Nonconforming situations should be evaluated against nonconforming use rules; any needed relief runs through variances and exceptions.

How overlays work in unincorporated Siskiyou County

• The County’s zoning plan lists combining districts (“B” districts), a Floodplain Combining District (“F”), and Fault‑Rupture Districts (“FR”) as part of the adopted district framework for unincorporated areas (§ 10-6.202 ).
• Overlay provisions add to, and may be stricter than, the underlying district. The F District expressly states that when combined with a companion zone, the more restrictive rule prevails (§ 10-6.5402 ). The Hemp Combining District likewise states its requirements govern in case of conflict (§ 10-6.6003 ).
• Some overlays incorporate separate countywide programs by reference. For example, floodplain development must meet flood regulations in Title 10, Chapter 10 in addition to any F District zoning standards (§ 10-6.5404; §§ 10-10.201, 10-10.202, 10-10.501–10-10.504 ).

District-by-district breakdown

Airport Environs (AE) Combining District

• Purpose: Protect public-use airports from incompatible encroachment and reduce noise/safety exposure for surrounding areas (§ 10-1.02 ).
• Applicability: Applies to land use changes, rezonings, land divisions, new construction, and certain height conflicts within the mapped airport “influence area.” Also applies to structures or trees taller than 200 feet AGL anywhere in the County (§ 10-1.03(a)–(b) ).
• Where it applies: Around County public-use airports (e.g., Montague‑Yreka Rohrer Field, Siskiyou County Airport, Weed Airport, Scott Valley Airport) as defined in the Chapter’s definitions and maps (§ 10-1.04 ).
• Typical permitted/limited uses: The AE overlay controls compatibility of otherwise allowed uses and building heights near airports; single-family homes on legal lots may proceed outside Compatibility Zone A if permitted by local regulations (§ 10-1.03(c)(2) ). Height limits and compatibility criteria are administered through this chapter’s standards (verify site-specific limits).
• Key dimensional/operational standards: Height and use compatibility standards apply within influence areas (specific numeric surfaces not found in retrieved materials). Expect FAA/Part 77-type height review triggers; verify with County.

Floodplain (F) Combining District

• Purpose: Protect public health, safety, property, and the environment in flood-prone areas and guide orderly long-range use of flood hazard lands (Article 54 statement of purpose; see also County flood program context in Title 10, Chapter 10) (§§ 10-10.104–10-10.108 ).
• Applicability: The F District layers on top of a companion zoning district; the more restrictive rule governs (§ 10-6.5402 ).
• Where it applies: Parcels mapped within the County’s adopted Flood Insurance Study and FIRMs, as amended by Letters of Map Change (§ 10-10.202 ).
• Typical permitted uses: Grazing, field crops, tree farming, utility lines/pipelines, and accessory ag storage/shelter buildings (but not residences or bulk fuel storage beyond stated limits) (§ 10-6.5402(a)–(c) ).
• Conditional uses: Public parks and recreation facilities, commercial feedlots/dairies, surface mining, flood control levees/dikes, and residential/commercial/industrial buildings or mobile homes if allowed in the companion zone and if they meet overlay standards (§ 10-6.5403(a)–(g) ).
• Key dimensional/operational standards: Companion zone dimensional rules apply unless superseded; special flood development standards must be met per the County Flood Damage Combining Ordinance and flood regulations (§ 10-6.5404; §§ 10-10.201–10-10.205, 10-10.501–10-10.504, 10-10.1101–10-10.1102 ). Examples include providing base flood elevation data where missing and submitting hydrologic/hydraulic analyses for certain encroachments (§ 10-10.501; § 10-10.502; § 10-10.504 ).

Fault-Rupture Zone (FRZ) Overlay District

• Purpose: Implement the Alquist-Priolo Act; designate and regulate development in Special Studies Zones along active faults for public safety (§ 10-6.5701; § 10-6.5702 ).
• Applicability: Applies as an overlay affecting all other zoning districts where mapped (§ 10-6.5701 ).
• Where it applies: Areas delineated by official State Special Studies Zone maps adopted by the County (§ 10-6.5702(a) ).
• Typical permitted/limited uses: No structure for human occupancy may be placed across the trace of an active fault, nor within 50 feet of such faults as shown in an FRZ (§ 10-6.5703(a) ). A geologic report by a California-registered geologist is required with development permits and subdivisions proposing structures for human occupancy (§ 10-6.5703(c) ).
• Key dimensional/operational standards: 50-foot minimum setback from active fault traces for structures for human occupancy; no change of use that converts a non-occupancy building to human occupancy unless it complies with FRZ standards (§ 10-6.5703(a)–(b) ). Specific lists of permitted uses within the FRZ are Not found in retrieved materials.

Mobile Home (M‑H) Combining District

• Purpose: Allow a second dwelling or a mobile home in lieu thereof in the Rural Residential Agricultural (R‑R) District when the M‑H Combining District is applied (§ 10-6.3301 ).
• Applicability: Only when combined with the R‑R District; all R‑R requirements remain in effect (§ 10-6.3302 ).
• Where it applies: Parcels zoned R‑R that carry the M‑H combining suffix on the County’s zoning map (verify site‑specific mapping).
• Typical permitted/limited uses: Placement of a second dwelling/mobile home consistent with M‑H and R‑R standards (§ 10-6.3301–.3302 ).
• Key dimensional/operational standards: Dimensional standards default to the underlying R‑R District; any special second‑unit standards formerly in Chapter 10‑6 apply only as codified today—verify current applicability.

Hemp (H) Combining District

• Purpose: Establish where commercial or research cultivation of industrial hemp may occur, and on what terms (§ 10-6.6004(A)–(B) ).
• Applicability and priority: The H District governs over conflicting rules in the underlying zone (§ 10-6.6003 ).
• Where it applies: Only on parcels mapped with the H Combining District (verify mapping with the County). The article references specific geographic areas for application; precise map boundaries should be confirmed with the Planning Division (Not found in retrieved materials).
• Typical permitted/limited uses: All uses normally permitted or conditionally permitted in the primary zoning district remain so in H, subject to all applicable code provisions (§§ 10-6.6005–10-6.6006 ). Cultivation of industrial hemp is permitted only in the H Combining District and requires a minimum parcel size of 80 acres (§ 10-6.6004(A) ).
• Key dimensional/operational standards: Compliance is required with Chapter 16 (Industrial Hemp Cultivation) and County licensing; additional setbacks and operational standards may be imposed there (§ 10-6.6004(B) ). For example, County hemp regulations address setbacks for indoor cultivation and licensing prerequisites (see Chapter 16 excerpts; zoning cross‑reference only) (§ 10-16.40 et seq. excerpts ).

Quick reference table: major overlays and their triggers

Practical guidance

• Start with your parcel’s base zoning and confirm whether any of the overlays above are mapped. The County’s zoning plan expressly includes combining and hazard overlays for unincorporated areas (§ 10-6.202 ).
• If you are in an F area, expect to submit flood data, base flood elevations, and possibly hydrologic/hydraulic analyses with your application, in addition to meeting your base-zone standards (§ 10-10.501; § 10-10.504; § 10-6.5403(e)–.5404 ). Coordinate early with staff on whether building code floodproofing standards are implicated alongside zoning; the County administers flood regs in conjunction with the California Building Standards Code (§ 10-10.104 ).
• In an FRZ, plan for a geologic report by a registered geologist and maintain a 50‑foot setback from active fault traces for any structure intended for human occupancy (§ 10-6.5703(a), (c) ).
• Within AE areas, height and use compatibility are the key checks; early scoping avoids late-stage conflicts with airport safety surfaces and noise compatibility criteria (§ 10-1.03(a)–(b) ).
• If your R‑R parcel carries an M‑H overlay, a second dwelling/mobile home can be pursued, but the R‑R dimensional and other standards continue to apply (§ 10-6.3301–.3302 ).
• For H overlays, verify acreage and licensing. Cultivation is prohibited outside H and must meet the 80‑acre minimum in H, plus Chapter 16 hemp rules (§ 10-6.6004(A)–(B) ).

Checklist

• Confirm base zoning and any mapped overlays for your parcel in the unincorporated area (§ 10-6.202 ).
• If in AE: identify airport “influence area,” applicable compatibility/height limits, and whether your proposal triggers AE review (§ 10-1.03(a)–(b) ).
• If in F: assemble floodplain submittals (BFE data, hydrologic/hydraulic analyses) and show compliance with flood development standards (§§ 10-10.501–10-10.504; § 10-6.5404 ).
• If in FRZ: retain a CA‑registered geologist; demonstrate 50‑ft fault trace setbacks for occupancy structures (§ 10-6.5703(a), (c) ).
• If parcel is R‑R with M‑H: verify eligibility and continue to meet underlying R‑R standards (§ 10-6.3301–.3302 ).
• If in H: confirm 80‑acre minimum and obtain County hemp license; comply with Chapter 16 hemp rules (§ 10-6.6004(A)–(B) ).
• Cross‑check general development standards, parking, and any needed design review or signage approvals for the proposed work.

Risks & Ambiguities

Plain-English Summary

If your unincorporated Siskiyou County parcel sits in an overlay, you must meet both the base zone and the overlay’s special rules—whichever is stricter. Near airports (AE), check height and use compatibility; in floodplains (F), plan on flood studies and possibly use limits; along mapped faults (FRZ), keep structures for people at least 50 feet off the fault and provide a geologic report; on R‑R lots with M‑H, a second dwelling can be allowed; in H areas, hemp cultivation is allowed only with large parcels and County licensing.

Source References

• Zoning plan and district list (unincorporated areas): § 10-6.201–.202
• Airport Environs Combining District (AE): § 10-1.01–.04
• Floodplain Combining District (F): § 10-6.5402–.5404
• County Floodplain Management Regulations: §§ 10-10.104–10-10.108; §§ 10-10.201–10-10.205; §§ 10-10.501–10-10.504; §§ 10-10.1101–10-10.1102; § 10-10.305
• Fault‑Rupture Zone Overlay District (FRZ): § 10-6.5701–.5703
• Mobile Home Combining District (M‑H): § 10-6.3301–.3302
• Hemp Combining District (H): § 10-6.6003–.6006 (with cross‑reference to Chapter 16)

Information Gaps

• AE numeric height surfaces/compatibility zone criteria: Not found in retrieved materials.
• FRZ “uses permitted” list beyond the stated limitations: Not found in retrieved materials.
• Specific official maps/boundaries for the H overlay areas: Not found in retrieved materials.

Retrieved passages

• CBC § 10 (Section 10-6.1515) High relevance show source text
• CBC § 10 (§ I) Medium relevance show source text
• Siskiyou County Zoning Code (TITLE 10.) Medium relevance show source text
• Siskiyou County Zoning Code (§ I) Medium relevance show source text
• Siskiyou County Zoning Code (§ 1) Medium relevance show source text
• Siskiyou County Zoning Code (§ I) Medium relevance show source text
• Siskiyou County Zoning Code (§ I) Medium relevance show source text
• Siskiyou County Zoning Code (article are) Medium relevance show source text

Cited sections

• Zoning plan and district list (unincorporated areas): § 10-6.201–.202 (§ 10-6.201)
• Airport Environs Combining District (AE): § 10-1.01–.04 (§ 10-1.01)
• Floodplain Combining District (F): § 10-6.5402–.5404 (§ 10-6.5402)
• County Floodplain Management Regulations: §§ 10-10.104–10-10.108; §§ 10-10.201–10-10.205; §§ 10-10.501–10-10.504; §§ 10-10.1101–10-10.1102; § 10-10.305 (§ 10-10.104)
• Fault‑Rupture Zone Overlay District (FRZ): § 10-6.5701–.5703 (§ 10-6.5701)
• Mobile Home Combining District (M‑H): § 10-6.3301–.3302 (§ 10-6.3301)
• Hemp Combining District (H): § 10-6.6003–.6006 (with cross‑reference to Chapter 16) (§ 10-6.6003)
• SiskiyouCounty_ZoningCode.md

• Official Siskiyou County code library