Almost every backcountry trip I've ever been on started with a map. When I was first figuring out how to travel in the backcountry in New Hampshire's White Mountains, those maps came from the Appalachian Mountain Club. These days if I'm looking at a map there's a 50% chance it's on a screen: Hillmap or Google Maps on my laptop, or a GPS app displaying a USGS quadrangle on my phone.
If I'm looking at a paper map of the Sierra it's pretty much guaranteed to be a Tom Harrison map. I think the first map of his I used was for Joshua Tree National Park. They're available everywhere in the Eastern Sierra (including some gas stations) and they're much more usable than USGS quads or National Geographic maps. The Atlantic has a short interview with him on their website right now.