David, I live in Kansas, but I've taken my 2004 Prius
to the high mountains of Colorado once (touring around Buena Vista) and to California three times using US 54 Wichita to Tumcumcari then I40 etc. on to LA and Bakersfield. No really big mountains, but the Prius performed like a charm. Plenty of snap and a pleasure to drive. No problms at all! The only negative aspect was on the long drawn-out, steeper grades, it seemed that the engine ran a little fast, but then I'm comparing it to a Buick Roadmaster 5.7 L. that made the same trek several times. To me, it is a great performer that keeps up with the biggies on the freeway - not to mention the 48 mpg average for over 3400 miles!!! One of those trips, we had three adults and two fairly large kids. Needless to say, that luggage space in back was over filled, but it all worked out!
Dick Monical