There are usually free maps of every US National Park. These are pretty basic, but do help in orienting yourself. I prefer using the maps that National Geographic makes for the parks. They are not specifically for bicycling, but are at a larger scale than the freebie maps, and are laminated to be water and tear resistant:
The state DOT (Department of Transportation) provides bike-specific maps for each region, so you'll need to know where exactly you are going. I've used them before and found them adequate but nothing thrilling. (This was six years ago, so things may have changed.) Links to these maps and other California maps here:
And if you are biking the Coast, I highly recommend getting the ACA maps.
Some links here:
As for New England, which states do you plan to be bicycling through?
Hope this helps!