Mark Powell wrote to us about a 1970 plane crash in which his wife's grandmother died. Mark wants to know if we have the coordinates to crash.

The short answer is disappointing, Mark. Our online map has dozens of points, but there is no assurance that any of them correspond with the crash you're researching. We're sorry.

Mark's research problem is pretty typical. Mark has the National Transportation Safety Board report on the accident, yet it does not contain the coordinates.

The problem illustrates one of our bigger headaches in this project. Nobody is the final authority on air crashes and the details surrounding them. Not the federal government, not the military, not the state and not any local agency that we could find.

For our online map, we have a list from the U.S. Air Force, which readily acknowledges the sites are only places where wrecks reportedly have not been cleaned up. The military has no idea of the details on most of them.

The NTSB database is interesting, but it, too, is far from complete. There were a slew of military crashes in the 1940s that are not included. And, as with any data collection, the information has holes as you look at crashes from decades ago.

For searchers in the field, the latitude and longitude coordinates are great starting points. But searchers say you need more than those coordinates for many crashes. A global positioning system, or GPS, unit comes in real handy in the Sierra -- this mountain range is simply a hulk of a natural resource.