The Central NP topos are compatible with 60csx. Do you have it on a CD?, because most Garmin map sets have unlock codes tied to the reciever. I believe it can be used on 2 receivers(?), but if not you have to purchase another unlock code to load it on additional receivers.
I do have it on CD so I don't believe their is a lock code involved. It would appear the 60csx uses microsd cards for data storage so I imagine you would download the National Park topos to a blank sd card?
Thanks Homero for the best price information on the 60csx. I am very tempted to grab the nearest credit card, but.... 
Wayne
Install a blank mircoSD in the 60CSX and load the CD to MAPSOURCE. Then transfer the mapset to the receiver from MAPSOURCE via USB.
And you don't need a huge MicroSD card. A 1gb card is plenty to hold several states data.