This is a Grade A+ arch on an official Class 1.3 trial (well-marked, level, official trail that is over 3-mile long with no climbing) when starting at Natural Bridge State Park, the trail is much shorter (Class 1.0 hike) if you start at the trailhead on Big Bend Road. Problem is, both trails put you on top of the arch at the narrows. To get under the arch, so you can see it, requires Class 3 climbing for ~20ft.
One my first trip to White’s Branch Arch, my wife and I saw no one the entire time from Natural Bridge. As soon as I climbed under the arch, we met people who had hiked from Big Bend Road; it was a little shocking to say the least.
The trail is clearly marked and very flat for the most part.