Heading westbound on I-84 (from Troutdale to Hood River, OR) exit the highway at the Starvation Creek State Park exit. Park, then walk to the west end of the parking lot. There you will find Starvation Ridge Trail #414. Take that and you will meet up with the Mt. Defiance trail within a half mile or so. Take the trail a short distance up the hillside and Lancaster will be part way up.
This is a shot of Lancaster Falls in the fall. It is a small, but neat little waterfall literally built into a hillside. This makes it pretty difficult to shoot, but it is worth it with the beautiful autumn colors.