Who Are Gateway’s LD & SP and Why Are Their Initials on This Structure? [PHOTOS]

A structure next to the Delores River just West of Gateway features these two sets of initials. Who do the initials belong to, and how did they wind up on this abandoned structure?

Just West of Gateway, Colorado, only a few thousand feet past the Colorado/Utah border, there exists an old one-room structure. The two sets of initials are located just above the front and only door. Who, or what, do the initials designate?

Unfortunately, time and the elements have taken their toll on the building. That, plus the fact the structure has been used a few thousand times for target practice, have left it in a dilapidated state.

To reach the structure, turn West at Gateway Canyons Resort at 4 1/10 Road, and continue West for several miles until you pass the Colorado/Utah border. Proceed another few miles. After reaching the bottom of a short and mildly technical hill, the structure can be spotted to the West not too far off the river.

What purpose did the structure serve? Do the initials LD and SP denote those who lived in or used the structure, or is this a ranch name?