A UAS operator reported flying in restricted airspace. When the operator realized they were in the airspace they landed immediately.

Narrative

I was at [the] ranch. Ranch located near Restricted Area R-XXXX (RA); some inside; some outside of Restricted Area. That morning; before sunrise; Person 1 saw a group of people walking in the dark. Called Person 2 to come and secure the area. Did not see them again. Later in morning fixing breakfast about XA:00 am Person 3 stated he saw someone walking in the brush. Also he said the buzzards had been circling nearby all morning. He asked if I could launch drone and check it out. I did so; flying two take-off for a total of about 10 minutes airborne; max altitude 40 feet. Person 4 walked up and asked if we were inside Restricted Area. It then occurred to me I was indeed inside RA. I landed immediately and put [the] drone away. I didn't think about it then but I would have imagined the area was inactive. Later we were advised by law enforcement; there were several groups of [people] transitioning the area. We are XX minutes to nearest public road and quite isolated. To say it lightly; we take trespassing seriously. In the moment; I forgot I was in RA and maybe flew where I was not suppose to. I should of called [the Control Agency] for status as I would have for any fixed wing flight. My Error. Won't happen again.