I should have mentioned that the camera I took backpacking was much heavier than other dSLR options: the Canon 20D. I generally brought a 17-40L lens, which is fantastic, and sometimes a 70-200 lens, which is rather heavy. I found that I used the 17-40 considerably more often than the 70-200. Part of this was due to lighting conditions, the 17-40L was a much faster lens (lower f stop) that produced rather pleasing shots in low light.
With the Sierra Nevadas your stomping grounds, I would suspect that there is ample opportunity to capture truly amazing photographs. A wide angle lens would be tops on my list, as well as good UV/Polarizing filters. A good filter to me is essential, as it does wonders to improve photographs, particularly on hazy days (think the moisture resulting from a melting snowpack). It also protects the lens. Break a filter and you are out $50; break the glass on your lens and you are our far more money.
One issue with the 20D was it was particularly susceptible to dust if you were not careful when changing lenses. It is a bummer to pull up your photos and find a dust spec in the middle of frame after frame. I am not sure how the latest cameras from the different makers handles this issue.
If I were to do it again, I'd look seriously at the primes. First they are often faster and lighter (less glass), and they do demand, in my opinion, a greater adherence to the art of composition than a zoom by their very nature of being a fixed focal length. If photo quality is the overriding issue, it is important to note that zooms do have a sweet spot, in terms of focal length/F-Stop. The 17-40L has very good glass and less distortion than typical zoom lenses, but it was still there. Finally, primes are often less expensive than high-end zooms.
I believe the Digital Rebel line offers terrific value, especially with the number of features offered. As you've already touched upon, you can spend a fortune on equipment. With the changes in sensors (the full frame capability is available on some prosumer and professional models), lens compatibility becomes an issue in the Canon line. The EF-S lenses are not full-frame compatible. Something to consider when buying a lens, since bodies may come and go, but lenses generally stay a part of your kit for years. The downside to any camera body that doesn't offer full frame capabilities is that the wide angle capabilities of a lens is effectively compromised.
The entire Nikon vs. Canon argument to me, anyhow, is pretty much tantamount to a religious debate. Each brand has its own advantages; many professionals stick by Canon because of the many lenses (just watch a sporting event on television) and because it was at one time well ahead of Nikon in the digital segment. Nikon has closed the gap and in some cases, exceeded Canon. I have photojounalist friends who swear by Nikon's spot metering system, for instance. I have used Nikon's DSLRs as well, and they are terrific. Speaking only as a rank amateur, I can guarantee that bad photos are a result of my poor technique, rather than any deficiency with the camera.
I wish you the best of luck. If you could borrow a camera and take it out on a few trips, all the better! I wish you the best of luck!