County profile · official public datasets

Siskiyou County, CA

421 public highway bridges tracked in the FHWA National Bridge Inventory: 39% rated Good, 55.6% Fair, 5.5% Poor.

421
Public bridges: 39%
Good condition: 5.5%
Poor condition

The verdict

According to the Federal Highway Administration's 2024 National Bridge Inventory.

Siskiyou County posts a better-than-median Poor-condition share among rated counties in the state across mid-size county bridge inventory.

Top 29%
lowest Poor share in state: 5.5%
Poor-condition share: 421
public highway bridges: 1971
avg year built

Poor is an FHWA condition category from the lowest applicable component rating (4 or below), not a live crossing-safety or closure decision. Rankings cover counties with at least five public highway bridges.

Siskiyou County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Siskiyou County ranks #17 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 5.5%). Siskiyou County, California contains 421 public highway bridges. Roughly 39% are rated “Good,” 55.6% “Fair,” and 5.5% “Poor.” Poor means the lowest applicable deck, superstructure, substructure, or culvert rating is 4 or below on the 0–9 NBI scale. It is a condition category, not a live safety or closure decision.

Responsible agencies inspect covered bridges on risk-based intervals under current NBIS rules and submit inventory data to FHWA annually. The list below shows every NBI-tracked bridge in the county. Use the “Sort by” controls to change the ordering, and click any row for its reported inspection date, traffic count, and condition fields.

Source: FHWA National Bridge Inventory. See methodology for full definitions.

Total bridges

421

Public highway bridges in Siskiyou County

Good condition

39%

164 of 421 rated 7-9

Fair condition

55.6%

234 of 421 rated 5-6

Poor condition

5.5%

23 of 421 rated 4 or below

In-state Poor-share rank

#17 of 58

Among California counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 421 NBI-tracked bridges by lowest applicable component rating.

Good

39% (164)

Fair

55.6% (234)

Poor

5.5% (23)

Siskiyou County's Poor-condition bridges carry 3,115 vehicle crossings a day

That is 0.4% of the county's reported daily bridge traffic on 5.5% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 135 crossings a day against 1,929 for a Good-condition one. A Poor rating is a condition category, not a closure or a live safety judgement; it means the lowest applicable component rating is 4 or below.

Computed over the 420 of 421 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

67.9% of Siskiyou County's bridges have passed the 50-year mark

286 of the 421 bridges with a recorded construction year were built in 1974 or earlier. Age alone is not a defect: a well-maintained older bridge can rate Good, and 39% of this county's inventory does. Even so, this older cohort is the population from which future Poor ratings are drawn, which is why the age profile below matters alongside the condition split above.

Cutoff derives from the 2024 release year minus a 50-year design life. Source: FHWA National Bridge Inventory, 2024 release.

One structure carries 19.7% of the county's Poor-condition bridge traffic

STATE ROUTE 96 over THOMPSON CREEK, built 1952, carries 615 vehicles a day, the most of any Poor-rated structure here. The county's Poor-condition exposure is concentrated rather than evenly spread, so the 23-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 3,115 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

2
1910s

5
1920s

8
1930s

10
1940s

9
1950s

47
1960s

134
1970s

106
1980s

42
1990s

20
2000s

29
2010s

6
2020s

3

What this shows Construction peaked in the 1960s, when 134 of the county's bridges still in the inventory were built, which is 31.8% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1971) matches the California average (1970).

How Siskiyou County compares with California's closest counties by inventory size

The 5 California counties nearest Siskiyou County in number of bridges, with their condition splits. Its 5.5% Poor share is the 1st-lowest of these 6. Its average build year of 1971 against a peer-group mean of 1968 is in line with the group.

Showing the 5 closest of 57 California counties eligible for comparison.

Bridge inventory size and condition shares for Siskiyou County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Imperial County	444	50.7%	40.5%	8.8%	1968
Butte County	437	31.8%	62%	6.2%	1958
Siskiyou County (this page)	421	39%	55.6%	5.5%	1971
Santa Barbara County	418	51.4%	42.8%	5.7%	1975
San Luis Obispo County	401	47.6%	46.6%	5.7%	1970
Humboldt County	396	38.9%	54.3%	6.8%	1968

Each share is of that county's own total tracked bridges; peers are the counties with 5 or more bridges whose inventory size is closest to Siskiyou County's. Source: FHWA National Bridge Inventory, 2024 release.

Nationwide counties with similar inventory size or average build year

Two NBI-derived peer sets for Siskiyou County, both outside California so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside CA (421 bridges here).

Fayette County, PA · 422 bridges
Kay County, OK · 419 bridges
Taylor County, TX · 419 bridges
Lewis County, WA · 419 bridges

Similar average build year

Nearest mean year-built outside CA (1971 here).

Wayne County, MI · avg 1971 · 1,026 bridges
Baltimore County, MD · avg 1971 · 783 bridges
Washington County, PA · avg 1971 · 655 bridges
Linn County, OR · avg 1971 · 566 bridges

Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.

All 421 Good 164 Fair 234 Poor 23

Fair-condition bridges (234)

Sort:

Siskiyou County Bridge Snapshot

Condition distribution

Siskiyou County's Poor-condition bridges carry 3,115 vehicle crossings a day

67.9% of Siskiyou County's bridges have passed the 50-year mark

One structure carries 19.7% of the county's Poor-condition bridge traffic

How Siskiyou County compares with California's closest counties by inventory size

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

Fair-condition bridges (234)

SCOTT RIVER RD

STATE ROUTE 263

INTERSTATE 5 SB

STATE ROUTE 96

INTERSTATE 5 NB

INTERSTATE 5 SB

CECILVILLE ROAD

ROUTE 5

INTERSTATE 5

INTERSTATE 5

INTERSTATE 5

INTERSTATE 5 SB

INTERSTATE 5 NB

INTERSTATE 5 NB

ABRAMS LAKE ROAD

INTERSTATE 5 SB

INTERSTATE 5

CECILVILLE ROAD

INTERSTATE 5 SB

INTERSTATE 5 SB

EDDYS GULCH ROAD

INTERSTATE 5 NB

E LENNOX ST

S5-N MT SHASTA OFF

INTERSTATE 5

U.S. HIGHWAY 97

STATE ROUTE 3

STATE ROUTE 3

STATE ROUTE 161

U.S. HIGHWAY 97

U.S. HIGHWAY 97

STATE ROUTE 96

INTERSTATE 5

STATE ROUTE 3

I-5 OFFRMP/KLAMATH

HIGHWAY 96

STATE ROUTE 161

GAZELLE-CALLAHAN R

HENLEY-HORNBROK RD

ISLAND ROAD

WALKER ROAD CONN

ISLAND RD

AGER BESWICK ROAD

HORSE CREEK ROAD

SCOTT RIVER RD

MOFFETT CREEK RD

OLD HWY 99

DUZEL CREEK RD

KLAMATH RIVER ROAD

COPCO ROAD

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