compass

[mikemanfra74]

If you are using a compass in the rocky mountains your magnetic declination will be ?

[Clanad]

In aviation it's known as "magnetic variation" and it's the angle between true north and magnetic north. The answer to your query depends where one is in the Rocky Mountains, since they extend from northern Montana to at least northern New Mexico, a distance of nearly 1,000 miles. A good average, however would be 12 degrees easterly variation (or "declination").

[johnlambert]

try here
http://www.ngdc.noaa.gov/seg/geomag/jsp/Declin ation.jsp