This 6 mile round trip hike is mostly on a lava field, the lava is called a’a. It looks a bit like freshly tilled earth from a distance, but is solid rock. The hike looks easy. It’s not. The trail is filled with loose rocks, and is very scrambly going indeed.
The sign is about a mile in. You can see the trail, and also how going off-trail would be difficult going indeed.
The brown areas are a lava flow from about 1790 on the foothills of 10,000 ft. Mount Haleakala.
The a’a piled in the front right is the ruins of a native Hawaiian structure from some centuries back.