Modoc County — Overlay Districts

Last reviewed: July 6, 2026

Overview

In unincorporated Modoc County, Title 18 – Zoning pairs each base (principal) zone with optional “overlay” districts that add location‑specific rules on top of underlying uses and standards. The County recognizes seven overlays: FH, EP, MP, M, AR, AH, and SP, each adopted on the official zoning and special zoning maps and enforced alongside base zoning across the unincorporated areas (§ 18.02.030.B; § 18.02.040.A–B) .

The single most important rule: Overlay zone regulations modify and supersede the principal zone standards on a lot, but only to the extent the overlay specifies (§ 18.02.070.E) .

Related topics you may also need to check: the County’s zoning, land use, development standards, parking, design review, historic preservation, signage, nonconforming uses, and variances and exceptions. Building and fire code requirements are addressed by the California Building Standards Code.

How the overlay system is organized

• The County adopts and maintains official zoning and special zoning maps showing where each overlay applies; amendments are reflected by the Planning Director (§ 18.02.040.A–D) .
• Overlays do not change permitted uses of a base zone unless the overlay sets a more restrictive rule; where rules conflict, the more restrictive one governs (§ 18.02.050; § 18.02.070.E) .

District-by-district breakdown (Overlays)

Flood Hazard (FH) overlay

• Purpose and where it applies. The FH overlay minimizes flood risk in FEMA Special Flood Hazard Areas (Zones A, AE, AH, AO, A1–30, A99) and any additional County‑mapped flood‑hazard areas; FH supersedes less‑restrictive base‑zone rules (§ 18.70.010; § 18.70.020) .
• Typical permitted uses. Uses remain those of the base zone, but development within FH must meet floodplain rules in Chapter 18.71 (e.g., elevation, floodproofing) (§ 18.70.020) .
• Key dimensional/technical standards.
  • Development permit in flood areas is required, with submittals documented by the Floodplain Administrator (§ 18.71.150; § 18.71.130–.140) .
  • Residential lowest floor must be at or above the base flood elevation; nonresidential must be elevated or floodproofed (§ 18.71.170.C) .
  • Manufactured homes and RVs have elevation/anchoring and time‑in‑place limits (§ 18.71.200–.210) .
  • Floodway encroachments are prohibited unless no rise is demonstrated (§ 18.71.220) .
  • Variances for floodplain management are tightly limited (§ 18.71.230–.250) .

Environmental Protection (EP) overlay

• Purpose and where it applies. The EP overlay protects wildlife habitat and environmentally sensitive or hazardous areas, and can be combined with LI, LIC, AE, RC, OFG, RR, and AG base zones; the M overlay is applied with EP to control minimum lot sizes and density (§ 18.74.010–.020) .
• Typical permitted uses. Base‑zone uses remain, but EP allows modification of minimum lot size and density to protect resources (§ 18.74.020) .
• Key procedural standards.
  • EP map amendments must identify the resource/hazard area, proposed development acres, and request the M overlay; multi‑unit projects also require a use permit (§ 18.74.050.A) .
  • Board must make findings that EP is necessary to protect the resource/hazard (§ 18.74.050.B) .
  • Development under EP must remain consistent with the General Plan and any specific plan (§ 18.74.030, § 18.74.050; consistency noted in § 18.74.010) .

Migration Protection (MP) overlay

• Purpose and where it applies. The MP overlay protects key antelope and deer migration routes/corridors by limiting encroachment, subdivision, and development; it is applied alongside base zones (§ 18.78.010–.020) .
• Typical permitted uses. Base‑zone uses are allowed unless they cause new encroachments that would impede migration; applicability is determined by the Planning Director with the Department of Fish and Game (now CDFW) site input (§ 18.78.030.A–B) .
• Key dimensional/technical standards.
  • MP corridors are configured case‑by‑case; generally a continuous corridor, and where a route is identified, a maximum of about one‑quarter mile on each side of the route is cited in the standards (§ 18.78.040.A) .
  • Exemptions include: legal existing buildings that do not substantially increase encroachment/intense human activity, and most fencing; when required, new fences may need to meet antelope fencing specs (§ 18.78.040.C–E) .
  • Exceptions to MP standards may be granted with specific findings (e.g., no compromise to route integrity; uniqueness of site conditions; or strict adherence would preclude all base‑zone uses) (§ 18.78.050.A–D) .

Minimum Lot Size (M) overlay

• Purpose and where it applies. The M overlay limits further subdivision to protect resources, reduce impacts, or preserve character; it specifies the minimum lot size that overrides the base zone (§ 18.82.010–.020) .
• Typical permitted uses. All base‑zone uses remain, but any future division must meet the M minimums (§ 18.82.020) .
• Key dimensional/technical standards.
  • The minimum lot size equals the property size at adoption or a designated size (e.g., M‑20 means a 20‑acre minimum); lot line adjustments/mergers may increase lot size for health/safety (§ 18.82.030) .
  • In practice M is often paired with EP, and the County requires M when using certain “one‑acre” or “five‑acre” agricultural division allowances so those exceptions don’t later multiply via further splits (§ 18.66.060 context for U; AE division conditions referencing M) .

Animal Restrictions (AR) overlay

• Purpose and where it applies. The AR overlay restricts animal keeping in medium/high‑density residential areas or other places where permissive animal keeping would be incompatible; by reference, AR overlays all RH (Residential High Density) areas (§ 18.86.010–.020; § 18.36.070) .
• Typical permitted uses. Routine domestic pets (e.g., dogs/cats) are allowed subject to nuisance limits; animal keeping beyond common pets is generally restricted per AR standards (§ 18.86.020.A–C) .
• Key dimensional/technical standards.
  • Lot size calculations for AR compliance must exclude road easements and consider contiguous area and barriers; detailed criteria apply (§ 18.86.030) .
  • Minimum lot size thresholds for animal keeping are specified in § 18.86.040 (Not found in retrieved materials).

Airport Hazard (AH) overlay

• Purpose and where it applies. The AH overlay implements the State Airport Approaches Zoning Law to prevent or remove hazards to flight operations around the County’s public‑use airports; lands within approach, transitional, horizontal, and conical zones are regulated per airport zoning maps (§ 18.90.010; § 18.90.030) .
• Typical permitted uses. Base‑zone uses remain unless they pose hazards; AH prohibits land uses that create glare, impair visibility, or interfere with radio communications, among other risks (§ 18.90.120) .
• Key dimensional/technical standards.
  • Height limits are tied to official airport elevations and surface slopes; for example, approach surfaces typically rise at a 20:1 slope and transitional surfaces at 7:1, with airport‑specific limits for Adin, Alturas, California Pines CSD, Cedarville, Eagleville, Fort Bidwell, and Tulelake (§ 18.90.040–.110) .
  • Nonconforming structures/trees may remain but can be required to add markers/lights; permits are required before altering or replacing nonconforming features (§ 18.90.130–.140; § 18.90.150) .

Specific Plan (SP) overlay

• Purpose and where it applies. The SP overlay identifies areas governed by an adopted specific plan; all base and overlay rules apply, but any use/development must also be consistent with the applicable specific plan (§ 18.94.010–.020) .
• Mapping. When a specific plan is adopted, the County amends the zoning map to apply SP to the plan area (§ 18.94.030) .

Quick reference table: Key overlay triggers and rules (unincorporated Modoc County)

Note: Where overlay rules and another standard conflict, the more stringent applies (§ 18.02.050; § 18.90.150) .

Checklist

• Confirm your parcel is in the unincorporated area and identify all overlays on the County’s zoning/special zoning maps (§ 18.02.040) .
• If in FH, prepare floodplain materials: BFE data, elevation certificates, and floodway analysis as needed (§ 18.71.150; § 18.71.170; § 18.71.220) .
• If in EP and proposing a map or multi‑unit project, include EP application elements and the companion M overlay request; demonstrate General Plan consistency (§ 18.74.050) .
• If in MP, coordinate early with Planning for the site determination; design to avoid encroachment and maintain corridor continuity; document any exemption or request an exception with findings (§ 18.78.030–.050) .
• If in M, verify minimum lot size (e.g., M‑20) before subdividing; plan line adjustments/mergers accordingly (§ 18.82.030) .
• If in AR or RH, check AR animal‑keeping limits and lot‑size calculation rules (§ 18.86.020–.030; § 18.36.070) .
• If in AH, measure proposed structure heights against airport surfaces and controls; evaluate light/glare/EM impacts; secure permits before altering nonconforming features (§ 18.90.040–.140) .

Risks & Ambiguities

Information Gaps

• EP overlay “Development standards” specifics in § 18.74.030: Not found in retrieved materials.
• AR overlay numeric minimum lot size/animal thresholds in § 18.86.040–.070: Not found in retrieved materials.

Plain-English Summary

Overlays are add‑on rules that sit on top of your base zoning in unincorporated Modoc County. If your land is in a floodplain (FH), near an airport (AH), along a wildlife migration path (MP), inside an environmental protection area (EP), limited to larger lots (M), or in a residential area with animal limits (AR), expect extra steps and sometimes stricter design, height, subdivision, or animal‑keeping limits—always in addition to the base zoning rules.

Source References

• Title 18 – Zoning: Overlays established; maps; effect; interpretations (§ 18.02.030.B; § 18.02.040; § 18.02.050; § 18.02.070.E)
• FH overlay purpose/coverage (§ 18.70.010–.020) and floodplain standards (§ 18.71.130–.220)
• EP overlay purpose/applicability and special provisions (§ 18.74.010–.020; § 18.74.050)
• MP overlay purpose, determinations, standards, and exceptions (§ 18.78.010–.050)
• M overlay purpose/regs/lot rules (§ 18.82.010–.030)
• AR overlay purpose/applicability/lot-size method; RH linkage (§ 18.86.010–.030; § 18.36.070)
• AH overlay airport zones, height limits, use restrictions, nonconforming/permits (§ 18.90.030–.140)
• SP overlay purpose/regs/mapping (§ 18.94.010–.030)

Retrieved passages

• Modoc County Zoning Code (title within) Medium relevance show source text
• Modoc County Zoning Code (Chapter 18.110) Medium relevance show source text
• Modoc County Zoning Code (Chapter 18.74) Medium relevance show source text
• Modoc County Zoning Code (Title 18) Medium relevance show source text
• Modoc County Zoning Code (section 18.71.150) Medium relevance show source text
• CBC § 11362.77 (Section 11362.77) Medium relevance show source text
• Modoc County Zoning Code (Chapter 18.144.) Medium relevance show source text
• Modoc County Zoning Code (Chapter 18.144.) Medium relevance show source text
• Modoc County Zoning Code (§ 18.74.040) High relevance show source text
• Modoc County Zoning Code (chapter shall) Medium relevance show source text
• Modoc County Zoning Code (section 18.100.020) Medium relevance show source text
• Modoc County Zoning Code (Chapter 18.20) Medium relevance show source text
• Modoc County Zoning Code (chapter and) Medium relevance show source text
• Modoc County Zoning Code (title by) Medium relevance show source text
• Modoc County Zoning Code (Chapter 18.100) Medium relevance show source text
• Modoc County Zoning Code Medium relevance show source text
• Modoc County Zoning Code (chapter shall) Medium relevance show source text

Cited sections

• Title 18 – Zoning: Overlays established; maps; effect; interpretations (§ 18.02.030.B; § 18.02.040; § 18.02.050; § 18.02.070.E) (Title 18)
• FH overlay purpose/coverage (§ 18.70.010–.020) and floodplain standards (§ 18.71.130–.220) (§ 18.70.010)
• EP overlay purpose/applicability and special provisions (§ 18.74.010–.020; § 18.74.050) (§ 18.74.010)
• MP overlay purpose, determinations, standards, and exceptions (§ 18.78.010–.050) (§ 18.78.010)
• M overlay purpose/regs/lot rules (§ 18.82.010–.030) (§ 18.82.010)
• AR overlay purpose/applicability/lot-size method; RH linkage (§ 18.86.010–.030; § 18.36.070) (§ 18.86.010)
• AH overlay airport zones, height limits, use restrictions, nonconforming/permits (§ 18.90.030–.140) (§ 18.90.030)
• SP overlay purpose/regs/mapping (§ 18.94.010–.030) (§ 18.94.010)
• ModocCounty_ZoningCode.md

• Official Modoc County code library