Richard, do you have the Caldor 7.5 Topo map? If so all you need now is a 7.5 Topo map ruler and you can get all 4 corner coordinates from the comfort of home. To save some money on maps in California, order them direct from the B.L.M., their phone # is 916-978-4400. For the map ruler go to www.MapTools.com and the ruler comes with instructions.
This is a quote from my G.P.S. manual, " NOTE: You should always be prepared and capable of navigating without the eTrex. It is designed to augment other forms of basic navigation, not entirely replace then." So in other words a map, compass and altimeter are still necessary tools.
One dose not have to be an expert, a basic understanding can come in handy if and when needed. This is the best help I can give at this time, without having the Caldor map. Ron