I didn't know the Indian Heaven area had so many. All I knew was that just south of Indian Heaven Wilderness there's a large lava field called, creatively, Big Lava Bed. I guess it is part of the Indian Heaven volcanic field but not the designated wilderness.

There's a forest road that runs along the east edge of the lava bed. One time I stopped and walked into it a little. It has vegetation and trees but the ground is very obviously a lava bed—very chaotic and rough, can tear up shoes, has sudden deep holes and trenches everywhere. It is very easy to get lost and definitely a bad idea to go in without a navigation plan. I went in only 50 yards or so, and that took a while. Here's a few photos I took: 1, 2, 3.

And here is a topo map of the area. Stands out on a satellite view. Interesting area, if rather dangerous to hike into. The forest isn't too thick, but it's enough to make it very easy to get disoriented.