Cascade Park and Fisher's Landing can have a lot of river rock (3/4" to 4 tons !!) Some areas are better, I have a friend on SE 34th right across from HP, that has had a nice orchard since 1950's.
I would excavate a 5' - 10' hole and replace the soil, and mound it for drainage. Since we have so much rain, the nutrients leach out, and need replacement, and lime., summers are quite dry, so a drip system is essential for getting a good start. (You might want to buy a place with trees, as it takes ~ 5 yrs to bear well). I've done some espalier trees, and it is very nice way to care for them. also consider a 'high density' planting on dwarf root stock. (trees, ~ 5' apart, and no more than 9 ft tall, and no branches longer than 2', preferably 12") You actually get more fruit per Sq ft.
Find some varieties that are scab resistant, as mold is the tough part on the west side of Cascades. (interestingly enough, the damage is done during bud and bloom season, when we are getting too much rain to spray frequently.) You also need firm apples, as we have Apple Maggot, and they like the soft varieties. (and pears too) Sweet cherries are pretty ez, and the birds really like them

Commercially, it is tough, because it will rain on June 20th, and split your whole crop, and they will mold... BTDT... Berries are the best and easiest. We have ~ 20 Blueberry bushes in our yard ~ 20-50 yr old plants are nice, and I got 10 of them for free last year, but had to go get them with our track hoe and dump truck (~ 500#, or 5ft root ball). They are different varieties (important for cross pollinate) and they are really pretty in the fall. (bright orange), EZ to care for, and they like the acid soils we have, same as rhodies. They just MUST be mulched to survive dry summer, and mounded to avoid drowning in winter.
generally Salmon Creek and Felida, Hazel Dell and Minnehaha are better soils. (and MUCH warmer) little east wind. I got a Clark County Soils map from the county extension service (I was a Master Gardener many years ago, and also an orchardist, as we had a 'u-pick' fruit farm with ~ 50 varieties of apples, pears, berries, cherries, peaches, plums...and a great garden - in south Hazel Dell)
these folks can help with fruit trees, They have several hundred varieties of free grafting stock at their scion exchange in the spring.
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