The California Department of Transportation (Caltrans), using federal funding and state funding with a grant from the Wildlife Conservation Board, is proposing a wildlife bridge crossing/wildlife exclusionary fencing project in Siskiyou County on U.S. 97 from post mile (PM) 18.0 to 22.4. The purpose of the project is to reduce wildlife/vehicle collisions and provide terrestrial species safe passage to improve landscape permeability and restore wildlife connectivity. The project is needed because U.S. 97 bisects important animal habitats for many species. Terrestrial mammals frequently cross the highway at grade to utilize the severed habitat. During the five years between 2015 and 2020, District 2 Maintenance staff reported clearing 50 deer and 16 elk carcasses hit by vehicles in the project area. This location is the District’s top priority on the animal crossing priority list based on the frequency of animals hit within the roadway. The proposed improvements include:
Wildlife Bridge Crossing
• Construct a wildlife bridge crossing over U.S. 97 at PM 19.77. The wildlife bridge crossing would be approximately 100 feet long and approximately 140 feet wide. Foundations for the new bridge would be concrete spread footings. Pile driving would not be required to install foundations for the wildlife bridge crossing. The bridge would receive architectural treatment to mimic the natural environment and to encourage use by wildlife. A metal sign would be installed to alert northbound traffic that they are approaching a wildlife crossing area approximately one-half-mile south of the wildlife undercrossing. In addition, a similar sign would be installed approximately one-half-mile north of the Grass Lake Rest Area for southbound traffic.
Wildlife Exclusionary Fencing
• Install wildlife exclusionary fencing along both sides of the U.S. 97 corridor from approximately PM 18.57 to 21.80. The height of the wildlife exclusionary fence would be approximately 8 feet.
• Remove any existing fence that is within Caltrans’ right-of-way that blocks the construction of the new wildlife exclusionary fencing. Temporary fencing near the bridge would be placed to prevent unwarranted free-ranging livestock from crossing the roadway/bridge during construction. Permanent low-profile fencing will be placed around both bridge approaches to prevent future ranging across the wildlife crossing and allow for the movement of local wildlife.
• A dry wildlife undercrossing (a culvert) would be installed at or near PM 18.57 to allow wildlife that have reached the southern terminus of the exclusionary fencing to cross safely under U.S. 97. The wildlife undercrossing would be 12 feet high by 12 feet wide and 80 feet in length and would be installed adjacent to an existing culvert that is approximately 4 feet in diameter and 143 feet in length. The method of installation would be cut and cover.
• Install wildlife escape ramps at various locations in the wildlife exclusionary fencing.
• Install 7 cattle guards at road connections to U.S. 97 (see Table 1 below).
Table 1. Locations of Cattle Guards
Road Connection West/East of U.S. 97 Post Mile (Approximate)
Miller Mountain Road West 19.38
Private road connection East 19.87
Private road connection West 20.15
Private road connection West 20.20
Private road connection East 20.21
Private road connection East 20.54
Private road connection East 21.70
• A 10-foot-wide corridor would be cleared of vegetation on both sides of the wildlife exclusionary fence.
Interpretive Display Stand
• An interpretive display stand would be installed at the Grass Lake Rest Area.
• A Transportation Management Plan (TMP) will be prepared for the project during the design phase.
• It is anticipated that lane closures and/or one-way reversing traffic controls would not be needed during the construction of the bridge abutments.
• It is anticipated that full closure of all lanes of U.S. 97 would be needed during the placement of pre-cast reinforced concrete box girders for the wildlife bridge crossing. Approximately 7 days of road closures would be needed, and full closure would generally occur in 20- to 30-minute increments within construction work hours during daytime only. A detour would not be provided as no alternative routes are available. If needed, there would be procedures in place during construction to allow emergency vehicles through the construction site.
• It is anticipated that lane closures and/or one-way reversing traffic controls would not be needed during the installation of wildlife exclusionary fencing because this activity would occur beyond the clear recovery zone.
• It is anticipated that one-way reversing traffic control would be utilized during the installation of the wildlife undercrossing at PM 18.57. Portable solar-powered traffic control signals would be temporarily installed on approaches to the construction zone at this location.
Staging/stockpiling may occur within the project limits at seven locations (see Table 2 below).
Table 2. Staging/Stockpiling Locations
Staging/Stockpiling Location West/East of U.S. 97 Post Mile (Approximate)
U.S. 97 (Grass Lake Vista Point) West 18.91
U.S. 97 East 19.61–19.71
U.S. 97 East 19.80–19.87
U.S. 97 West 19.88–19.95
U.S. 97 East 19.88–20.00
U.S. 97 (Grass Lake Maintenance Station) West 20.10
U.S. 97 (Grass Lake Roadside Rest Area) West 21.80
The project would not utilize a disposal site. Fill material to build the embankments of the wildlife bridge crossing would be obtained from two on-site borrow sites located along U.S. 97 from PM 19.60 to 19.75 (one borrow site is located west of the roadway and the other borrow site is located east of the roadway). Any excavated material from bridge work will be utilized as embankment material on the west/eastside of the proposed wildlife bridge crossing.
Construction of the project would disturb approximately 4.18 acres of topsoil. Maximum excavation depths are estimated at approximately 20 feet and would be associated with the construction of bridge abutments and wing walls.
Tree removal would be required at borrow sites, at the wildlife bridge crossing, and within 10 feet on both sides of the wildlife exclusionary fencing.
Construction of the project would not add new utilities or require the relocation of existing utilities.
Most of the proposed work would occur inside Caltrans’ right-of-way. However, some work would occur outside Caltrans’ right-of-way on private property. Construction of the project would not require the permanent acquisition of additional right-of-way.
Federal land owned by the United States Forest Service is present within the project limits on U.S. 97 from approximately PM R16.0 to R16.4, 19.9 to 20.0, and 22.8 to 23.5, but there is no underlying Forest Service land within Caltrans’ right-of-way at these locations. The project limits border land owned by Union Pacific Railroad from approximately PM 19.79 to 20.06, 20.9 to 21.1, and 21.70 to 21.80. No work is proposed on land owned by the Forest Service or Union Pacific Railroad.
Temporary construction easements (TCE) would be required for work occurring outside Caltrans’ right-of-way. It is anticipated that land surrounding the wildlife bridge would be protected through a conservation easement or purchase and subsequent preservation by a wildlife conservation group.