Generally, maps for adventure races are USGS quads, 1:24K or 1:25K. Sometimes they are custom maps from MyTopo or other similar providers (still 1:24 or 1:25k).
The maps are divided up into 1K squares based on the UTM coordinate system. Take a look at Maptools.com
. They do a good job explaining UTM's.
Sometimes, the maps have a printed UTM grid, others have only the grid intersections printed, but most often, the maps will only have UTM tick marks on the border of the map. If the grid isn't there, I add it with a straight edge and a fine tip permanent marker. I suppose that with just the corners marked, you could plot the coords, but a small mistake can cost a lot of time (a lot more than it takes to draw the grid!).
The (CP locations are usually provided as a list of UTM coordinate pairs which must then be plotted on the map(s). You use a UTM corner tool to pinpoint the position within the 1K block.