Where I hunt, a backup is necessary. Lots of mountain lions. A hunter just made the front page of our newspaper the other day that was attacked by a mountain lion. If it hadn't been for his pistol, he wouldn't of lived to tell the story. I wouldn't carry anything less than a .45 caliber as backup. The problem with mountain lions, is that they see you long before you see them...and they usually pounce on your back...not the easiest angle to shoot a rifle with any accuracy!!! LOL...I just pictured that in my mind.
Don, the Ruger P-series is a great line of pistols. I own a P-89 (which is a 9mm model) and it has never so much as jammed, and I've put somewhere around 1000 rounds through it. It's a solid gun, but bulky. I would recommend the Springfield XD .45ACP if you're wanting something that meets the 4" barrel minimum and can still be concealed. You can get it in a full frame size or medium, and they come in different barrel lengths. I have one, and it weighs a lot less that my P-89, is considerably more slim, and is a better shooter, PLUS, it has a tactical rail that I have an XD light attached to. I have six pistols all together, and it's the first one I would grab in a bad situation. Here's a pic of it...