This 1:20 000 Gem Trek recreation map and guide for the Lake O'Hara area in Yoho National Park provides both a detailed trail map and detailed trail descriptions.  It is really all you need to get the most out of your visit.  The map has a contour interval of 25 metres, and includes the UTM grid so that you can use it with your GPS. 

If you are travelling more widely in the Rocky Mountain National Parks, we carry the complete line of Gem Trek Recreation Maps.