The Western Red Cedar is one of the giants of the northwest. There are few old growth cedar stands left, but when you do come across one, you'll find giant trees that are over 1000 years old. There happens to be one such stand on Moscow Mountain, but it's not very well publicized. Please respect the land here and practice Leave No Trace ethics so that the forest here will continue to thrive for years to come.
There are other old-growth cedar groves nearby in Elk River, where you can find the largest tree east of the Sierra-Cascades divide, and in the Hobo Botanical Area near Clarkia, Idaho. Here's a list of caches at some of these other cedar groves.
The hike to the cedars begins at the lower Tamarac Road parking area (winter parking). If the gate is open, you can knock about a mile off of your journey by parking at the upper parking area, but currently the gate is closed. The hike is approximately 2.25 miles one-way (4.5 round trip) and can be combined with GC5WN0M to make a 5.6 mile round-trip hike. There are other trails leading to this spot, so you might be able to come up with an alternative route that is shorter.
You are looking for a brown painted nalgene bottle. I hope you enjoy this place as much as I do.