I actually just attended the Oregon Truffle Festival last month, which is an amazing event if you want to learn more about truffle hunting when it comes around again next January. I learned a little bit about truffle-hunting, but you’ll probably have to seek out a true pro for expert advice. Here’s what I can tell you:
*Oregon white truffles grow underneath Douglas fir trees. They like stands of trees that are between 15-30 years old. I am not aware of a white Douglas fir variety (though I’m not a botanist!) There is a tree known as the white fir, but that is a different species. White fir: http://plants.usda.gov/factsheet/pdf/fs_abco.pdf; Douglas fir: http://plants.usda.gov/plantguide/pdf/cs_psme.pdf
*They can be anywhere near the root system of the tree, so yes, they can be farther out from the tree. They can be anywhere from an inch under the soil to much deeper.
*They are in season now although it may be tapering off. They are ripe in the winter months and tend to be at their peak around January.
*As far as where to hunt them around Cottage Grove, I’d contact your local forest service office to find out about public lands where you can hunt them. You have to be careful about hunting them on private land—make sure you have permission from the land owner before you go out. Some private land owners have contracts with professional truffle hunters and lease the foraging rights on their land.
Cottage Grove Ranger District: 541-767-5000. Also, truffle hunting now requires a permit, so talk to your ranger about that as well.
Here is a great video that will give you a visual and a ton of good information about what Oregon truffle-hunting looks like: https://www.youtube.com/watch?v=0zkv0KKJbYg
The gentleman featured in the video is Jack Czarnecki, owner of Oregon Truffle Oil and an expert on Oregon truffles.
Another good resource if you want to learn is to go out on a foray with a professional hunter, like Kris Jacobsen of Umami Truffle Dogs in Eugene. (http://umamitruffledogs.com/) The other benefit hiring a truffle guide to take you out is that many of them use a dog to hunt. When you hunt with a dog, vs. raking, you are guaranteed to find ripe truffles, because the ripe ones give off the aroma that attracts animals. (Unripe truffles may ripen over time if stored in a container in the fridge, but ripe truffles have the true truffle aroma and are immediately ready for use).
I was lucky enough to go out on a truffle hunt at the truffle festival this year, and it was a really neat experience. Good luck to you—I hope you find some!