A full-resolution version of the map is available for download [1] as a PDF (1.8 MB).
Links:
[1] http://sonoranheritage.org/docs/Map_SonoranDesertHeritage.pdf
[2] http://sonoranheritage.org/docs/Map_SonoranDesertHeritage.pdf
[3] http://sonoranheritage.org/docs/Map_SonoranDesertHeritage.pdf
[4] http://www.adobe.com/go/getflash