This map shows the broad area where wildlife dispersing East/west from the Trinity Alps, Russian, Siskiyou and Marble Mountain Wilderness complexes are blocked by the interstate 5 road corridor. Seasonal migration of large mammals would preferably travel unimpeded into roadless comp,exes East of I 5 in the Shasta National Forest to the Lassen National Park and Great Basin.
These linkages probably go from the Shasta Springs on the northern edge to the northern edge of Shasta Lake at Lakehead. Interestingly one of the most useful linkages follows the Pacific Crest Trail down the Castle Crags park complex and cross I 5 eastward to the McCloud basin into Mt Lassen Park.
I have personally observed approximately 10 black bear carcasses in this small zone over the last 15 years while traveling on Highway 5.