This is the NPS ranger station; BLM has a sign outside, as well, though I didn't see any BLM people when we were there.
There were two rangers present when we visited. It's a very nice ranger station, with static and audio / visual displays.
The Holland America buses stop here to let people use the array of portable facilities and to visit the ranger station. Just to the left of this building, you can see the edge of the new (and as yet unopened) rest room facilities.