A few weeks later Jerrie and I went back to check it out. That day we only did a one-half to one mile unofficial hike through a gate marked "no tresspassing" (we were just dummies since we were following some other people). After that we just did the .5 mile easy trail ("John Nagle Nature Trail"). Although we were not suppose to be on that first trail, hopefully this will some day be open to the public thus giving this area some decent hiking options.
Since I knew there was a longer, open-to-the-public trail located there, a month or so later I went back on my own to check it out further. I attempted to do the "Woods Tour Trail" but ended up doing a brief uphill loop. After ending up back at the trailhead, I did the hike again, this time starting out on the road. I found that the trail actually crosses the road (a second time) and continues on from there. Over all its a pretty interesting hike, albeit short at only a couple of miles. Definitely worth it for a quick hike since it was only a dozen miles from my front door to the trailhead. The trail is suprisingly steep in sections thus making it a decent trail run I bet. There seems to be extensive trail opportunities and some are already unofficially established making it a series of confusing intersections at times.
I found finding details on the trails somewhat difficult. Not much in the way of "official maps" but I did find a little map and info on oregonlive -
Oregon Live info

Found this rough topo on some lasertag site -
topo of Magness
Sounds like the tree farm is the location for some lasertag event?
Directions to Magness Memorial Tree Farm -
Travel on I-5 to exit 283.
Turn west on Wilsonville Rd.
Travel four miles to Edminston Rd. and turn right.
Travel 1.3 miles to SW Ladd Hill Rd. and turn right.
The tree farm is 1/2 mile down the hill on your left.