I almost never attempt to catch spring Chinook, but there are scads of them coming into the lower Columbia and Willamette basins right now. Many more Chinook than steelhead are in the rivers. Since you are here, you might as well give them a shot - Sandy or Clackamas would be good venues. I haven't a clue how to catch them, but I hear that early in the day, slow deep water, they can be had. Locally, winter steelhead are spawning or spawned and the summers seem to either be late or low in numbers. That is, steelhead fishing is s-l-o-w. I'd bet that a goodly number of those dink trout you've seen are really steelhead smolts. It is surprising how large a fly they can stuff in their mouths.