Not while riding I haven't, but a friend and his girlfriend and my now ex- girlfriend and me ran into something like that. We were hiking and came up to a slash pile. We started walking around when we heard a nice deep growl/howl. My freaking skin crawled when I realized what was making it. Not fifteen feet from us there was a good size mountain lion just staring us down from inside the slash pile. Naturally me and my buddy jumped between it and the girls (I was really thinking "oh shit, take the girl just leave me alone!"

) Anyway I drew my Glock 22 (.40 cal) and my buddy pulled out his kitty stopper the .357 mag. We backed away and just went right back down the hill. I will admit I was scared shitless.