There's a large parking lot at the Jerusalem Mill on Jerusalem Road. At the back of the lot is a large field with a path along the edge by the forest. Take the third entrance on your left, which is the trailhead for Jerusalem Mill Trail (blue-blazed). If you jump on too early and find yourself on the white-blazed Little Gunpowder Trail
, keep an eye to your right where you'll cross the blue trail.
This trail is a climb through the forest away from the river. You need to be a rock garden lover to tackle this trail. There are lots of rocky, rooty technical sections along this entire trail. Some short, steep climbs with rocks and roots will challenge your endurance and focus. After about a mile, you'll meet back up with the white-blazed LGP trail.