Marshall–Petaluma Road
Rolling ranch country between the Tomales Bay side and inland Marin, with crests and changing visibility.
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Road shape
- Length
- 10.9 mi
- Bends
- 43
- Switchbacks
- 0
- Bends per mile
- 3.9
- Turning per mile
- 373°
- Curviest rank
- 56of 85
Measured from the OpenStreetMap centreline at a 20 m sampling step — road shape only, not a safety or speed judgement. How bends are counted.
Elevation
- Total climb
- 1,703ft
- Climb per mile
- 156ft
- Highest point
- 759ft
- Steepest grade
- 8.3%
Sampled every 100 m from USGS 10 m elevation data, a public-domain federal dataset. Total climb counts vertical change in both directions, so it does not depend on which way you drive. How elevation is measured.
Speed limits
40 mph
Published limits
40 mph in the documented section; check signs elsewhere.
Marin’s 2024 bridge-project RFP describes a posted 40 mph road at the project area. This does not verify every section.
Posted signs always govern. How speed evidence is handled.
Sources
Difficulty 2/3 (Winding) is our editorial rating of width, bends and sightlines; “Medium speed” describes character, not a target speed. Full method. Identified from:
- Bay Area Riders Forum · Scenic roads ↗
- Rennlist · Bay Area road discussion ↗
- OpenStreetMap road data ↗ (11 ways in this trace)
Reviewed 2026-09-08. The trace shows selected road sections, not a navigation route.