US Bridges

SR 77 over Mammoth Wash

Fair

Pinal County, Arizona · 3.6 MI N JCT Old SR 76 · Structure no. 00493

Built
1956
69 years old
Condition
Fair
inspected February 2025
Type
Slab
Concrete Continuous
Length
144 ft
6 main spans
Daily traffic
3,653
2022 count
Owner
State
State Highway Agency

About this bridge

SR 77 over Mammoth Wash is a concrete continuous slab carrying SR 77 over Mammoth Wash in Pinal County, Arizona. It was built in 1956, so it is 69 years old, older than the Arizona average of 47.8 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 5 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

It carries about 3,653 vehicles a day, roughly 15% of them trucks, projected to reach 8,164 by 2042. The structure is 144 ft (43.9 m) long and 45 ft wide. If it were closed, the detour would be 24.2 mi (39 km).

Location

Open in Google Maps
CarriesSR 77
CrossesMammoth Wash
Location3.6 MI N JCT Old SR 76
RouteState Highway 77
CountyPinal County
StateArizona
Coordinates32.7005, -110.6439
Functional classRural Minor Arterial

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionFebruary 2025
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating41 US tons
Inventory rating24 US tons

Structure

Structure typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans6
Design loadHS 20
Structure length144 ft (43.9 m)
Longest span25 ft (7.6 m)
Deck width45 ft (13.7 m)
Roadway width40 ft (12.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,653 (2022)
Projected traffic8,164 by 2042
Trucks15%
Lanes on structure3
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed24.2 mi (39 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$1,000 (2025 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SR 77 over Mammoth Wash built?

It was built in 1956, making it 69 years old in 2025.

What condition is SR 77 over Mammoth Wash in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in February 2025.

How much traffic does SR 77 over Mammoth Wash carry?

About 3,653 vehicles per day (2022 count), of which roughly 15% are trucks.

How long is SR 77 over Mammoth Wash?

The structure is 144 ft (43.9 m) long with a longest span of 25 ft (7.6 m) and a deck 45 ft wide.

Who owns SR 77 over Mammoth Wash?

It is owned by the State Highway Agency.