One factor they track (p.80) is "Quality of geological data base (includes quality and scale of maps, ease of access to information, etc.)" 83% of respondents gave Arizona the top two ratings in this category. Colorado, New Mexico, and Utah had slightly higher numbers but the percentage who gave them 1's was less than for Arizona.
The Canada-based "Fraser Institute has conducted an annual survey of metal mining and exploration companies to assess how mineral endowments and public policy factors such as taxation and regulation affect exploration investment. Survey results represent the opinions of executives and exploration managers in mining and mining consulting companies operating around the world.""The survey now includes data on 72 jurisdictions around the world, on every continent except Antarctica, including sub-national jurisdictions in Canada, Australia, and the United States."
http://www.fraserinstitute.org/researchandpublications/publications/7276.aspx