In the post Historical Items of interest | Old Lookout Photos on the sidebar there is a link to Collowash Mountain, which shows it is most likely a seasonal lookout site, like Baty Butte, which is also listed. I will see if I can find the old Firemens Maps for Collowash Mountain. I have one with Baty Butte shown with the label L O. Nearby peaks that had a Fire Tower were marked in addition with a red stamp of a L in a circle.
Collowash Lookout Panoramas