Trinity County — Overlay Districts

Last reviewed: July 6, 2026

Overview

In unincorporated Trinity County, Title 17 Zoning uses several overlay and combining districts that add standards on top of a parcel’s base zone. These overlays often respond to scenic resources, flood hazards, historic character, water supply/quality, or federal recreation area rules. The overlays below govern what you can build, where, and how—alongside the base zoning and countywide development standards.

Overlays in Trinity County do not replace the underlying zone—they layer extra triggers, permits, or performance standards that must be met in addition to the base zoning.

How overlays are shown

When an overlay applies, its code abbreviation is appended to the base zone on the County’s district maps—for example, an “SC” suffix indicates the Scenic Conservation Overlay applies on top of the base district per § 17.25.020 . Similarly, the CWR overlay appears after a base zone on the map per § 17.29A.010(A) .

District-by-District

Scenic Conservation Overlay — “SC”

• Purpose and where it applies:
  • Identifies areas with “unusual scenic qualities” and places controls on building placement, roads, and vegetation management in those areas per § 17.25.010 .
  • Applied where: within the 100‑year floodplain of public waterways; within 50 feet of County-designated scenic highways; and along streams designated as scenic waterways in the General Plan, per § 17.25.020(B)(1)–(3) .
• Typical permitted uses:
  • All uses allowed by the underlying zone remain allowed; however, a Planning Director Use Permit (PDUP) is required for listed activities within the portion of the parcel that carries “SC,” per § 17.25.030 .
• Key review scope and standards:
  • PDUP review is limited to: building location; public/private road or driveway development; decks/boat landings/wells/accessory improvements; and vegetation removal (with limited hand‑tool removals exempt), per § 17.25.040(A)–(D) .
  • If a Timber Harvest Plan or CEQA/NEPA document already analyzed the work, a separate PDUP is not required per § 17.25.050 .
• Notes:
  • If a use also requires design review or signage approvals by its base zone, those still apply.

Critical Water Resource Overlay — “CWR”

• Purpose and where it applies:
  • Applied by the Board of Supervisors, after hearing, wherever development could detrimentally affect water resources through over‑extraction or contamination, per § 17.29A.010(B) .
  • “CWR” appears after the base zone on maps; it is in addition to the underlying zone requirements per § 17.29A.010(A) .
• Typical permitted uses:
  • Uses allowed by the base zone continue, provided they conform to the overlay, per § 17.29A.020 .
• Key standards (subdivision and potable supply focus):
  • Water quantity: before any parcel division, prove a year‑round supply to each new parcel via one or more of the following: an on‑site well at least 100 ft from any stream and drilled to at least 50 ft producing ≥1.5 gpm; a qualifying spring producing ≥1.5 gpm; or a compliant public community water system, per § 17.29A.030(A)(1)–(3) .
  • Water quality: proof of safe drinking water prior to division; the Health Department may require certified chemical and bacteriological analysis, per § 17.29A.030(B) .
  • Exception: divisions that would not necessitate water use may be marked “CWRN” and are ineligible for building/septic permits until conditions change, per § 17.29A.040 .

Flood Hazard (FH) Zoning District

• Purpose and where it applies:
  • Applies to mapped special flood hazard areas, including FEMA regulatory floodways/AE zones; certain A zones (e.g., along the Trinity River or in mapped communities); one‑hundred‑year floodplains identified on recorded maps, by entitlement, or by approved studies; and Trinity River “maximum fishery flow” areas, per § 17.29B.050(A)–(F) .
• Typical permitted uses:
  • By right (outside floodways): agriculture without structures that obstruct flood flows; wire/wood fencing that passes water; maintenance/repair of existing bridges/culverts/roads; small‑scale recreational mining not subject to SMARA, per § 17.29B.060(A)–(D) .
  • With Floodplain Development Permit (Director): e.g., new or replacement crossings, levees, bank protection if certified for no harmful cumulative rise; substantial improvements to existing structures; or new structures only where no building site exists outside FH, all subject to § 17.29B.070 and standards in § 17.29B.130 .
  • With Use Permit (Planning Commission): SMARA mining (with seasonal restrictions), per § 17.29B.080 .
• Floodway restriction:
  • Encroachments in regulatory floodways are prohibited unless a licensed engineer certifies no rise in base flood elevation; if met, all FHO standards also apply, per § 17.29B.090(A)–(B) .
• Development standards:
  • FH areas use the same development standards as the Flood Hazard Overlay (see below), per § 17.29B.100 .

Flood Hazard Overlay — “FHO”

• Applicability:
  • Applies to FEMA AO or AH shallow‑flooding areas and FEMA A zones not already in FH, per § 17.29B.110 .
• Permitted uses:
  • All base‑zone uses may proceed, but a Floodplain Development Permit is required before construction or any other County entitlement, per § 17.29B.120 .
• Key development standards (selected):
  • Anchoring and flood‑resistant construction required and certified by a registered architect or engineer; manufactured homes must meet anchoring standards, per § 17.29B.130(A) .
  • Materials/methods must minimize flood damage; utilities located to prevent floodwater intrusion; provide slope drainage paths in AH/AO, per § 17.29B.130(B) .
  • Elevation: residential lowest floor must be at least 2 ft above BFE in A/AE/AH/A1–30, or in AO at least 2 ft above mapped depth (or 4 ft above highest adjacent grade if no depth shown); elevation certified upon completion, per § 17.29B.130(C)(1)(a)–(b) .

Special Treatment / Special Treatment Area — “ST/STA” (Historic Overlay)

• Purpose and where it applies:
  • Protects cultural/historic resources; may be applied to National Register sites and to other owner‑nominated sites upon Board approval; mapped as “ST” or “STA” and explicitly identified as an overlay zone, per § 17.29C.010 and § 17.29C.020 .
  • Countywide districts are described (Districts I–III) for administration, per § 17.29C.030(A)–(C) .
• Typical permitted uses and standards:
  • Not found in retrieved materials.
• Related permitting notes:
  • Some uses (e.g., cannabis storefront retail) add a Conditional Use Permit when sited on parcels with “ST,” and trigger recommendations by an architectural review committee to ensure compliance with the historic program, per § 17.43H.020(B) .
  • See Trinity County Historic Preservation for broader policy context.

Recreation Development District — “RD‑1” (treated as an overlay in other chapters)

• Purpose and where it applies:
  • Governs development in the Trinity Unit of the Whiskeytown‑Shasta‑Trinity National Recreation Area, balancing private use with recreation/resource conservation and federal acquisition rules, per § 17.26.008 .
  • Although created as a base district in Chapter 17.26, other chapters refer to an “RD‑1 overlay zone” for special procedural constraints (see Variances below), per § 17.31.010(E) .
• Typical permitted uses:
  • By right: one single‑family dwelling; accessory buildings; necessary utilities; timber management/renewable resources, per § 17.26.010(A)–(D) .
  • By use permit: motels/hotels/resorts/campgrounds; limited commercial tied to “C” districts or resorts; limited industrial only when consistent with “I” and without adverse impacts; public utilities; and signs with size limits, per § 17.26.020(A)–(E) .
• Key procedural standard:
  • Variances within the RD‑1 area require permission (or a finding of no need) by the U.S. Secretary of Agriculture before County approval, per § 17.31.010(E) .
• Other cross‑rules:
  • Certain uses are categorically disallowed in RD‑1 (e.g., cannabis nurseries), per § 17.43A.020(B)(1) .
  • Major home occupations in “SC,” “FH,” or “RD‑1” overlay areas need a use permit, per home‑occupation rules in Chapter 17.30B (table excerpt) .

Special Building Site Area Combining Districts — “B‑1”, “B‑2”, “B‑3”

• How they work:
  • “B” districts combine with a base zone and replace that zone’s minimum building site area and parcel width; they’re applied and administered under Chapter 17.30, per § 17.28.010 .
• Key dimensional standards:
  • B‑1: 10,000 sq ft minimum parcel area; 100 ft minimum width, per § 17.28.010(A) .
  • B‑2: 15,000 sq ft minimum parcel area; 100 ft minimum width, per § 17.28.010(B) .
  • B‑3: Minimums as specified on the zoning map, per § 17.28.010(C) .

Quick-Reference Table (selected overlays)

Practical notes that affect projects

• Overlays are layered: your project must meet both the base zone and overlay requirements. Where conflicts occur, the overlay chapter often prevails for its subject matter (e.g., flood safety) .
• Overlay triggers often add permits, not necessarily prohibit use. For example, “SC” doesn’t change base uses but requires a targeted PDUP for site placement/vegetation work in the overlay area, which can be just a portion of a parcel per § 17.25.030 .
• Some overlays interact with other county processes. For example, variances in the RD‑1 area require federal clearance under § 17.31.010(E)—a wrinkle you won’t see in most zones . See Variances and Exceptions.

Checklist

• Confirm your parcel’s base zone and any overlay suffixes on the County zoning map (e.g., “SC,” “CWR,” “FHO,” “B‑1”) per § 17.04.010 and overlay applicability sections .
• If in an SC area, scope whether your work (building placement, access roads/driveways, docks/wells, vegetation removal) requires a Planning Director Use Permit per § 17.25.040 .
• If in CWR, assemble water quantity/quality evidence before any parcel division per § 17.29A.030; consult the Health Department for required tests .
• If in FH or FHO, obtain a Floodplain Development Permit and design for anchoring/elevation/materials compliance per § 17.29B.120–.130; check latest FEMA FIRM mapping .
• If in ST/STA, expect added scrutiny; some uses need a CUP and architectural review recommendations per § 17.43H.020(B); coordinate early with design review .
• If within RD‑1, verify allowable uses and note that any variance also requires Secretary of Agriculture permission per § 17.31.010(E) .
• If mapped with a B‑1/B‑2/B‑3 combining suffix, apply the “B” minimum lot area/width instead of the base zone’s per § 17.28.010 .
• Coordinate other applicable rules—parking, landscaping and screening, signage, and any nonconforming uses—because overlays don’t waive them.

Risks & Ambiguities

Plain-English Summary

If your unincorporated Trinity County property has an overlay, you still follow your base zoning—but you also meet the overlay’s extra rules. Scenic areas add a light permit focused on siting and vegetation; water‑sensitive areas may require proof of supply before land divisions; flood areas require elevation/anchoring and a Floodplain Development Permit; historic overlays can add a CUP and design oversight; RD‑1 areas have special use lists plus federal sign‑off for variances. When in doubt, verify your map suffixes and talk to County staff early.

Source References

• Title 17 Zoning plan, districts, and maps: § 17.03.010, § 17.04.010
• Scenic Conservation Overlay (SC): §§ 17.25.010–.050
• Critical Water Resource Overlay (CWR): §§ 17.29A.010–.040
• Flood Hazard District/Overlay (FH/FHO): §§ 17.29B.050–.100, §§ 17.29B.110–.130, § 17.29B.090
• Special Treatment (Historic) Overlay (ST/STA): §§ 17.29C.010–.030; cannabis CUP overlay trigger: § 17.43H.020(B)
• Recreation Development (RD‑1): §§ 17.26.008–.020; RD‑1 variance condition: § 17.31.010(E); cannabis nursery prohibition in RD‑1: § 17.43A.020(B)(1)
• Special Building Site Area Combining Districts (B‑1/B‑2/B‑3): § 17.28.010(A)–(C)

Retrieved passages

• Trinity County Zoning Code (§ 1) High relevance show source text
• Trinity County Zoning Code (Chapter 17.25) High relevance show source text
• Trinity County Zoning Code (chapter is) High relevance show source text
• Trinity County Zoning Code (Title 17) Medium relevance show source text
• Trinity County Zoning Code (chapter shall) Medium relevance show source text
• Trinity County Zoning Code (§ 1) Medium relevance show source text
• Trinity County Zoning Code (§ 1) Medium relevance show source text
• Trinity County Zoning Code (§ 3) Medium relevance show source text
• Trinity County Zoning Code (chapter shall) Medium relevance show source text
• Trinity County Zoning Code (§ 1) Medium relevance show source text
• Trinity County Zoning Code (Section 17.25.040) Medium relevance show source text
• Trinity County Zoning Code (Chapter 17.26) Medium relevance show source text
• Trinity County Zoning Code (§ 1) Medium relevance show source text
• Trinity County Zoning Code Medium relevance show source text

Cited sections

• Title 17 Zoning plan, districts, and maps: **§ 17.03.010**, **§ 17.04.010** (Title 17)
• Scenic Conservation Overlay (SC): **§§ 17.25.010–.050** (§ 17.25.010)
• Critical Water Resource Overlay (CWR): **§§ 17.29A.010–.040** (§ 17.29A.010)
• Flood Hazard District/Overlay (FH/FHO): **§§ 17.29B.050–.100**, **§§ 17.29B.110–.130**, **§ 17.29B.090** (§ 17.29B.050)
• Special Treatment (Historic) Overlay (ST/STA): **§§ 17.29C.010–.030**; cannabis CUP overlay trigger: **§ 17.43H.020(B)** (§ 17.29C.010)
• Recreation Development (RD‑1): **§§ 17.26.008–.020**; RD‑1 variance condition: **§ 17.31.010(E)**; cannabis nursery prohibition in RD‑1: **§ 17.43A.020(B)(1)** (§ 17.26.008)
• Special Building Site Area Combining Districts (B‑1/B‑2/B‑3): **§ 17.28.010(A)–(C)** (§ 17.28.010)
• TrinityCounty_ZoningCode.md

• Official Trinity County code library