Horse Hill Trail

Work on Horse Hill Trail is complete. The trail is open to visitors. The improved trail serves as a gateway via Bob Middagh Trail to open space lands heading west.

A steep fall line trail along a PG&E gas line easement had emerged from years of social use. Due to substandard design and alignment, the trail eroded over time, discharging sediment to creeks and storm drains, affecting visitor safety.

• Improve trail sustainability
• Improve visitor safety

• Realign Horse Hill Trail, as a contoured trail with a ten percent grade.
• Improve drainage with a culvert to reduce sediment in streams.
• Decommission nearby undesignated social trails to preserve ecosystem and habitat.

• 2015: Project Identified
• 2016: Project Planning
• Summer 2016: Community Outreach
• Spring 2017: CEQA Review
• Summer 2017: Construction
• August 2017: Work Complete

On August 25, 2016, the Marin County Open Space District (MCOSD) hosted a community workshop in Mill Valley. Parks staff and community members discussed the proposed Horse Hill Trail and Bob Middaugh Trail projects in Alto Bowl Preserve. A feasibility study presented alternatives for addressing severe erosion and improving visitor access to Horse Hill Trail. 

• Horse Hill Trail Feasibility Study pdf

The August 25, 2016 meeting was followed by a 30-day comment period which closed on September 24, 2016.  

Several options were considered for this project. After an exhaustive evaluation process, the MCOSD moved forward with recommending the realignment of Horse Hill Trail at a 10% grade and decommissioning of the Gasline Trail.

The CEQA evaluation compared environmental impacts associated with the proposed project to those identified in the 2014 Road and Trail Management Plan Environmental Impact Report, to determine if new information, changed circumstances, or new environmental effects required revisions to the mitigation measures, as described in CEQA Guidelines Section 15162. The analysis found that the project met the conditions for application of State CEQA Guidelines Section 15162 and preparation of a new EIR, addendum, or negative declaration was not necessary.

• Consistency Analysis
• Notice of Determination

This project required permits and/or approvals from:

• California Department of Fish and Game
• California Regional Water Quality Control Board
• United States Army Corps of Engineers
• Tribal Heritage Preservation Office