These photos show a very small portion of the 700+ acre Big Obsidian Flow. These shiny black rocks (actually very dark glass) were formed when lava flowing from the volcano hardened as it cooled. As you can see by the top photo, the Flow is very tall, rising high above the mature trees.
While walking on the path up to see this area I came across one of the small butterflies I had seen yesterday (dead, unfortunately). I have added a second photo to that post (just a few down from this one) so if you have seen the original post already you may want to take a second look at it.