Total bridges
109
Public highway bridges in Mariposa County
County profile · official public datasets
Mariposa County, CA
109 public highway bridges tracked in the FHWA National Bridge Inventory: 21.1% rated Good, 67.9% Fair, 11% Poor.
- 109
- Public bridges
- 21.1%
- Good condition
- 11%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Mariposa County pairs a higher-than-median Poor-condition share among rated counties in the state with an older average build year than the state inventory.
- 49th
- of 58 on Poor share
- 11%
- Poor-condition share
- 109
- public highway bridges
- 1956
- 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.
Mariposa County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Mariposa County ranks #49 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 11%). Mariposa County, California contains 109 public highway bridges. Roughly 21.1% are rated “Good,” 67.9% “Fair,” and 11% “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.
Good condition
21.1%
23 of 109 rated 7-9
Fair condition
67.9%
74 of 109 rated 5-6
Poor condition
11%
12 of 109 rated 4 or below
In-state Poor-share rank
#49 of 58
Among California counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 109 NBI-tracked bridges by lowest applicable component rating.
Good 21.1% (23)
Fair 67.9% (74)
Poor 11% (12)
Mariposa County's Poor-condition bridges carry 10,890 vehicle crossings a day
That is 6.8% of the county's reported daily bridge traffic on 11% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 908 crossings a day against 1,839 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 109 of 109 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
80.7% of Mariposa County's bridges have passed the 50-year mark
88 of the 109 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 21.1% 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 42.7% of the county's Poor-condition bridge traffic
STATE ROUTE 140 over MILES CREEK, built 1928, carries 4,650 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 12-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 10,890 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Mariposa County's bridges were built
109 bridges with a recorded construction year, grouped by decade
- 1910s 5
1910–1919
5 bridges
- 1920s
1920–1929
20 bridges
- 1930s
1930–1939
12 bridges
- 1940s
1940–1949
9 bridges
- 1950s
1950–1959
15 bridges
- 1960s
1960–1969
22 bridges
- 1970s 6
1970–1979
6 bridges
- 1980s 5
1980–1989
5 bridges
- 1990s 4
1990–1999
4 bridges
- 2000s 6
2000–2009
6 bridges
- 2010s 3
2010–2019
3 bridges
- 2020s 2
2020–2029
2 bridges
What this shows Construction peaked in the 1960s, when 22 of the county's bridges still in the inventory were built, which is 20.2% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year is 1956, 14 years older than the California average of 1970.
How Mariposa County compares with California's closest counties by inventory size
The 5 California counties nearest Mariposa County in number of bridges, with their condition splits. Its 11% Poor share is the 4th-lowest of these 6. Its average build year of 1956 against a peer-group mean of 1967 is 11 years older.
Showing the 5 closest of 57 California counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Tuolumne County | 125 | 36% | 56.8% | 7.2% | 1964 |
| Sutter County | 121 | 33.9% | 52.9% | 13.2% | 1968 |
| Mariposa County (this page) | 109 | 21.1% | 67.9% | 11% | 1956 |
| Lassen County | 108 | 25.9% | 65.7% | 8.3% | 1968 |
| Calaveras County | 105 | 33.3% | 60% | 6.7% | 1962 |
| Del Norte County | 96 | 51% | 37.5% | 11.5% | 1975 |
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 Mariposa 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 Mariposa County, both outside California so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside CA (109 bridges here).
- Boone County, IL · 109 bridges
- Gove County, KS · 109 bridges
- Hodgeman County, KS · 109 bridges
- Trigg County, KY · 109 bridges
Similar average build year
Nearest mean year-built outside CA (1956 here).
- Philadelphia County, PA · avg 1956 · 585 bridges
- Cochise County, AZ · avg 1956 · 501 bridges
- Hampden County, MA · avg 1956 · 428 bridges
- Washington County, MD · avg 1956 · 300 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
All bridges (109)
TRIANGLE ROAD
PoorOver: SNOW CREEK
0.1 MI W DARRAH RD, Mariposa, CA
Built 1935 Load: 15.2 t ADT: 360
OLD TOLL ROAD
PoorOver: BEAR CREEK
3.0 MI W OF SR 49, Mariposa, CA
Built 1948 Load: 17.8 t ADT: 130
MARY HARRISON MINE
PoorOver: MAXWELL CREEK
AT SH 132, Mariposa, CA
Built 1926 Load: 18.8 t ADT: 10
STATE ROUTE 140
PoorOver: MILES CREEK
10-MPA-140-3.64, Mariposa, CA
Built 1928 Load: 24.0 t ADT: 4,650
6TH STREET
PoorOver: MARIPOSA CREEK
AT STROMING ROAD, Mariposa, CA
Built 1950 Load: 24.3 t ADT: 1,080
BUCKEYE ROAD
PoorOver: MARIPOSA CREEK
2.3 MI S/O OLD HWY, Mariposa, CA
Built 1947 Load: 30.5 t ADT: 200
STATE ROUTE 140
PoorOver: SWEETWATER CREEK
10-MPA-140-37.83, Mariposa, CA
Built 1926 Load: 31.8 t ADT: 1,400
STATE ROUTE 140
PoorOver: SLATE GULCH
10-MPA-140-37.09, Mariposa, CA
Built 1926 Load: 36.0 t ADT: 1,400
USONA ROAD
PoorOver: MIDDLE FK CHOWCHILLA RIV
2.2 MI SOUTH OF SR 49, Mariposa, CA
Built 1970 Load: 59.3 t ADT: 190
Read our methodology - how this data is sourced, computed, and verified.
Related
Data sourced from official public datasets. See our methodology for details. Retrieved and formatted by PlainBridges
Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.