You have quite a few good choices here, Tim. It all depends on the exact feature set you desire.
A typical example of whats available is the Mountain Hardwear Backcountry Recon Pant ($195; www.mountainhardwear.com). These use Mountain Hardwears proprietary Conduit waterproof-breathable laminate, a material thats on par with Gore-Tex for waterproofing and pretty close in breathability. These are well-designed pants, with nearly full zips, pockets, reinforcing patches at high-wear areas, and adjustable cuffs to keep out snow. They weigh about a pound.
For something lighter, try Outdoor Researchs Celestial Pants ($139; www.outdoorresearch.com). These use Gore-Tex PacLite, a light, two-ply version of Gore-Tex that offers excellent performance at the cost of some loss of durability. They have half zips, which help with layering and save some weight over full zips. They add only eight ounces to your load, which is wonderful. And Id say durability is fine for the activities you describe. I just wouldnt do too much groveling around in the mud and gravel.
PacLite is a popular pant materialI think because most makers realize people dont really wear their rain pants as much as they do rain jackets. I know I sure dont. It really has to be coming down before I pull on rain paints. ArcTeryx is another company that uses PacLite, in its Alpha SL pants ($199; www.arcteryx.com). They have sealed cuffs, side zips that go nearly to the top, and reinforcements at the instep. Of course, ArcTeryx also makes pants with full three-ply Gore-Tex XCR, but the Beta ARs will cost you $325.
I also like REIs Taku Pants ($159; www.rei.com). They use Elements, an REI-specific material for waterproofing and good breathability, plus theyre pretty durable with three layers of material. I have a Taku Jacket ($199) and think its a very fine piece. And there are the L.L. Bean Stowaway Pants ($129; www.llbean.com), an excellent bargain considering theyre a full Gore-Tex pant. They have only short zips though.
I shouldnt think length is too much of an issue. Im your height and most fit pretty well. The REI Taku, however, is available in a 30-inch inseam.
Get more advice from the Gear Guy as he picks this seasons top gifts in Away.coms Holiday Gift Guide. Youll probably find a few things to put on your own wish list, too.