After crossing the road from South Side
, you continue on the trail for approximately 0.1 miles before there's a fork in the trail. Stick to the left fork as the right takes you down to the road. You'll stay on this for a bit longer before encountering another fork.
This time, stay right to continue on Jack's Route -- going left takes you up Moose Marbles
. The end of Jack's Route comes at a switchback that when you turn has a steep uphill with a tree root in the trail a few feet up -- that is the beginning of Switch Blade.