Fiddleheads are young ferns, still curled up. Some varieties of fiddleheads are edible, including the Bracken Fern (Pteridium aquilinum), which can be found here in southern Oregon, and is also distributed around the world. All ferns need moisture though, as they are spore-bearing (like mosses). Ferns are considered to be “in between” the lower plants (such as mosses) and the higher plants (flowering plants), because they still reproduce by spores, but they are vascular plants.
The Pacific Northwest has over 50 species of ferns, 7 of which are common in Oregon: bracken, sword, maidenhair, lady, deer, spreading wood, and licorice. To identify ferns in the Pacific Northwest, I highly recommend the following resources:
Plants of the Pacific Northwest Coast, by Pojar and Mackinnon
This is a great field guide, especially if you know your flowering plant families. It is comprehensive, with quality pictures, life history (and other interesting) information, and is easy to use. Even if you don’t know your flowering plant families, you will be able to use the section on ferns. You can buy it on Amazon, and probably most nature bookstores/nature centers in the PNW.
Ferns to know in Oregon, by the Oregon State Extension Service
I found a copy of this in a visitor center in Brookings, OR, and absolutely love it. It is a small (4.5″ x 3″, approx.), thin booklet that weighs next to nothing and can fit in your pocket. It has the name of the most common ferns that can be found in Oregon, a silhouette picture, and some natural history information. As OSU says here, you can buy this bulletin (EB 785) for 50 cents/copy. Or you may be able to pick it up in a visitor center.