The Siskiyou Mountains in Southern Oregon and Northern California are beautiful, rugged, and remote. While the Bigfoot Trail passes through here and uses many of the existing trails and roads. However, due to the remoteness of the area there are some sections where you will need to use a map, compass, and your orienteering skills in order to find your own path between trails.
In this particular spot, there is not a defined path connecting the Bigfoot Trail as it crosses Grayback Road. You may find hints of old logging and fire roads that can be helpful in these areas, just be careful not to follow them blindly and double check with your maps so you don't end up off trail.