Big Beaver Trail is a 42 mile trail located near Marblemount, WA that features beautiful wild flowers and is rated as moderate. The trail is primarily used for hiking and is accessible from June until September.
Directions from Rainy Pass: Drive 24 miles west on Highway 20 to the Ross Dam Parking area near mile marker 134. Park in the lot on the northern side of the road.
My wife and I did this trail in the summer of 2011 as a modified loop trail (in conjunction with the Little Beaver Trail and a $125 prearranged boat ride). The trail is extremely well managed and taken care of. We ran into to two different troops of people that were doing trail maintenance. There are several campsites along the trail with pre made tent pads and fire rings. Being in the North Cascades National Park, a permit is required to overnight camp, which is available free of charge on a first come first served basis. Campsites have a limited number of pads and are therefore limited to the number of people they will allow to stay in any given site. We actually only stayed in our chosen site once, as we overestimated our abilities and did not make our mileage each day.
As stated above the trail is well maintained and relatively smooth for the most part. Livestock are allowed on the trail up to Beaver Pass, so there are quite a few piles of evidence on the trail. When we crossed over Beaver Pass there was still about one - three feet of snow on the ground which made trail navigating a bit sketchy. I followed animal prints and looked for cut trees (the only trees cut in National Parks are generally ones that fall over trails).
Water was easy to come by and at some points problematic. That year they had a late winter and the melt was in full force by the time we hiked. Expect wet feet, it's not called The Cascades for nothing. Most bigger, well established streams will have a bridge of some sort to aid in crossing.
Firewood was not easily found. The rangers prefer you not wander into the natural environment too far (in order to keep from damaging the ecosystem). What wood we could find was generally either too wet or rotted. We were able to make a campfire each night, though a not very impressive one.
The mosquitoes had just started coming out two weeks prior to us getting there, according to the rangers. Being from Southern Louisiana my wife made a bold statement when she said "I have never seen mosquitoes like this before." They were fierce. To the point that by the last day, we were almost running to keep them off us. Bring plenty of repellent, something we did not do.
There were not a whole lot of grand scenic spots due mostly to heavy tree cover. The ones we did see, were majestic.