Pecan forest for Western Washington?

I have 5 acres That I am arranging to lease to a nonprofit group to plant a food forest and build tiny houses. During the winter I went to pick up my wife at the hospital in Tacoma Washington and as I walked from the car to the hospital there were Pecans sprouting in the ditch alongside the sidewalk. I brought some home and put them in one of my starter flats. They are now in 3 gallon nursery pots.
We need a plan for setting them out in a permanent location. Anyone with Pecan experience?
We have any kind of soil available from gravel to clay. The land has a SE slope. The West side is shaded from the evening sun by a fir forest. It was loged a few years ago and is now covered in Scotch broom and blackberries.

I have plenty of experience with them -- as weeds. Since my neighbors have so many, I don't need any on my property, but the squirrels don't share my plan. They put them in my hugelkultur, my onion bed, the kitchen herb garden, etc.

You may want to get them out of the 3 gallon pots and put them in the deepest pot you can find. Around here, young pecan trees are kept in plastic pots that have a height equal to 3 or 4 times their diameter. No, they are not stable and have to be supported to stay upright, but they allow the tap root to develop properly. Once the tap root develops, you can't kill the seedling, it keeps coming back (from my experience).

I would say plant them in a clay soil. They love the Georgia clay and when you get to the western extent of their range, in the arid west, they still flourish in river valleys with lots of clay in the river bed. Pecans (and walnuts, a close relative) are sensitive to late frosts. Usually, they are the last trees to leaf out in the spring, when the danger of frost is well past. As long as you don't have any late freezes, like can happen in higher elevations, they should do well for you.

Because you're fairly far north, seedling pecans might not end up maturing crops consistently - it depends on the length of a given season, and on the genetic heritage of those pecans. Also the weather - since they are originally adapted to the hot humid summers of the south east. There are far north growing pecans that can ripen even in southern Ontario, but they are smaller nuts. That said, I was just talking to a nut grower that said pecans make great root stock (as long as they are hardy) because they put out side roots and produce a small tree faster. They can be grafted with hickories and some hicans (pecan/hickory hybrid), if those produce a better nut in your region.

There are a couple of pecan varieties selected for growth in the northwest. They are sold at http://www.burntridgenursery.com/Northern-Pecan/products/59/. I bought all their varieties for planting in my Sierra orchard.

I would be as well, Hans.  I no longer live in Western WA, but researched the idea at the time.  Learned it was a non starter, due to the number of "heat days".  For those interested pecans need so much time above a certain temp, 85 degrees I believe, to set nuts, much like fruit trees need chill hours below 45.  I believe most varieties of Pecan need 1000+ hours to set fruit.  Walnuts on the other hand can be quite productive west of the Cascades.  

Sadly I gradually lost all the plants from the nuts that sprouted due to neglect and misplacing them.  I am quite confident that with our current climate conditions they would produce nuts. As I mentioned the nuts were from trees that line the street opposite St. Joseph Hospital in Tacoma WA. They do have the advantage of the city heat and on the transition from the plateau to the slope to the harbor so they do not get early or late frost.  We have been consistently getting 80 to 90 degree days for many years now during June through August.  I seldom get across the sound to Tacoma now so I do not know how those trees are doing. Even though we are further north we are rated as the same climate zone as the Carolinas where pecans are plentiful on the homesteads I watch on YouTube.