Boy, do I have a pant for you. Its the Arcteryx Gamma LT pant (arcteryx.com), which uses a stretch-woven fabric from Schoeller to create a lightweight, tough pant that has a remarkably wide comfort range. Ive worn it this spring in temps from the mid-30s to low-70s, and it has been warm or cool as conditions dictate. Id take it up Mount Rainier with little more than a pair of light wool long underwear to put underneath. The pant has also stood up to glissading, sliding down gravel slopes, banging into rocks, and more. And it looks great: very trim and sleek, with low-profile zippers. Fine for around town.
Arcteryx Gamma LT pant
Gamma LT pant
But, the bad news is the price: $150. I do think the Gamma LT is worth it because its so versatile and well-made, but I concede that is a chunk o change for a pair of pants.
Arcteryx does make another pant called the Agent Comp, which is a tough, soft-shellish sort of pant that goes for $99. Is it as nice and versatile as the Gamma LT? Ummm .no. But its a nice pair of pants!
Heres a thought: Take a pair of Ex Officios excellent Amphi Pants ($60; exofficio.com). Its a light, comfortable nylon pant thats great for hiking or around town. Take some Patagonia Capilene One (formerly known as Silkweight) leggings ($36; Patagonia.com) to wear under them and extend the comfort range on cool days.
Convertible pants mark you as a turista" as surely as a baseball cap and white sneakers, but Mountain Hardwears Convertible Pants ($100; mountainhardwear.com) are comfortable, durable, and decent-looking. Again, take the Capilene One stuff for a layer underneath.
Have a great trip!