As I understand it, and its been a while since I made my inquiry, you do in fact need reservations for large groups. However, its was also explained to me that even if you have reservations you CANNOT turn anyone away if they show up. My memory is a little fuzzy on this but I think you ahve to go through the Hood River Crag Rats to make reservations. I wanted it over christmas one year and was told that a family had laid claim to it over the holidays for several years now.
Ask Nonanon--he would be the man with the information.