Hanging millipede

"Don't touch this," our guide said. She was pointing at a fallen branch covered with small, purplish-brown leaves. "Some people are allergic to it," she added. We clustered around, looking, but keeping our distance.

Frullania nisquallensis, "Hanging millipede liverwort".

It's not a moss, but a liverwort*. It grows on alder and maple; in this particular bit of forest, the large deciduous trees are mostly maples. And it may cause contact dermatitis, which gives it an alternate name: "Woodman's eczema".

Good to know, if you're scrambling about in the rain forest. I Googled it and read a few reports; contact with the wet bark or with fallen fragments of the liverwort can cause an eczema that lasts several weeks. Gloves are no protection, unless they're waterproof and no water seeps in through the wrists, but most eruptions are on the face and other exposed areas. It seems to be no problem in dry weather.

Frullania nisquallensis, commonly known as Hanging millipede liverwort, is a reddish-brown species of liverwort in the Jubulaceae family. It is found in western Washington and British Columbia, including Vancouver Island. The plant grows in mats, sometimes in mats that hang from tree branches (particularly those of alders, or maples), or growing close to the substrate. (Wikipedia) (My emphasis)

That explains the "hanging" part of the name, "hanging millipede." It doesn't look much like a millipede to me, though. There's a whole page of photos on INaturalist, which may be helpful if you're planning to go looking for firewood on a wet day. But stay dry!

*More on this, later.