Pretty much as far north on the Oregon coast as you can get, right at the mouth of the Columbia River. I just pulled out the road atlas and the little town west of Astoria is Warrenton. Fort Stevens State Park is on the little spit of land to the north of Warrenton. Once you get to Fort Stevens State Park, there are signs to direct you to the various points of interest, including the wreck of the Peter Iredale. Try to time it so that you'll be there at low tide and that way you'll get the best views from any angle that you might want to see it from.