saw my first wild cougar

The German Shephard/Mastiff? cross and I were high up when I heard a loud pounding downhill. I caught a glimpse of a big tan animal with a long tail that was raised up and white on the underside. The dog had enough brains to come right back when I whistled for him because he was about 2/3rds the size of it. I asked my host when she came back what deer had long tails. After talking about it for about 5 minutes she decided I saw a cougar.