During the first world war, Woodrow Wilson authorized a crash program to produce wooden steamships to ferry supplies to the American Expeditionary Force in Europe. Over 700 ships were authorized but less than 100 built by the war's end. Yet the program continued for several more years, producing hundreds of leaky, inefficient, and unwanted vessels before Congress cut off funding. Eventually over 150 of the ships were towed to Mallows Bay on a remote section of the Potomac. Many were burned to the waterline and the rest slowly sank into the shallow water. Over 100 years later, their outlines are clearly visible from the air, as you can see on Google Maps. (Note: This post is shamelessly stolen from this great post at Metafilter, which contains links to other goodies like some kayaker's pictures of the wrecks). I recently used this in class and was rewarded with a collective gasp from the students as they saw the outlines of the wrecks come into view!
So what long-gone historical landmarks in the Northwest are still visible (or only visible) from the air and discoverable through Google Maps and similar services? I don't have time to hunt any down right now but possibilities include the Mullan Road, old railroad cuts, sunken docks and other facilities (a quick look at Seattle on Google Maps reveals some suggestive structures under the water). The problem however, as is so often the case with Google Maps, is that the resolution of the photos for much of the mountain west is very poor. (I was at a Google Earth teacher workshop at Eastern Washington University earlier this year. While the teachers from Spokane ooh-ed and aah-ed as they picked out their own cars in their driveways, the teachers from little towns like Republic and Usk stared at the pixellated blur on their screens and cursed their fate.)
Google is constantly updating and improving the resolutions avaialble. But currently the most promising use of this technology at present is to look for signs of history in the places Google cares about the most. Can anyone think of possble histori relics near Hood River?