The AZ law creates a new definition of trespassing:
A. IN ADDITION TO ANY VIOLATION OF FEDERAL LAW, A PERSON IS GUILTY OF TRESPASSING IF THE PERSON IS BOTH:
1. PRESENT ON ANY PUBLIC OR PRIVATE LAND IN THIS STATE.
2. IN VIOLATION OF 8 UNITED STATES CODE SECTION 1304(e) OR 1306(a).
http://www.azleg.gov/legtext/49leg/2r/bills/sb1070s.pdf
It gives law enforcement the legal cover to apprehend "suspicious" persons....with no legal standard of what constitutes suspicious.
Think about it...any person in AZ can now be charged with trespassing by simply standing on any public or private property IF (#2) they cannot prove (by carrying papers at all times) they are a citizen or legal resident.