I've been hearing about the Oregon White Truffles for a long time, and finally decided to get into them this year. After some research, I zeroed in on areas with fir trees in the 20 to 45 year old range. I look for places where the ground is covered with moss or duff, but little or no undergrowth, similar to where I usually look for Chanterelles. In the coast range, I've stayed under 1,000 ft elevation; in the Cascades, I've extended that to 1,500 ft. Places where rodents - squirrels and chipmunks - have been digging are a great sign that there are some truffles around.
I use a clam rake, but in my experience you don't have to rake deep - they're right under the surface. They look like little new potatoes and are rock hard. Ripe truffles are darker brown in color, while the un-ripe ones are whiter. (editor's note: shallow raking is also less damaging to the mycelia of mushrooms like Chanterelles, which may also be sharing the same habitat!)
More of Tizzy's truffles.