Define "probable cause". The law says A LAW ENFORCEMENT OFFICER, WITHOUT A WARRANT, MAY ARREST A PERSON IF THE OFFICER HAS PROBABLE CAUSE TO BELIEVE THAT THE PERSON HAS COMMITTED ANY PUBLIC OFFENSE THAT MAKES THE PERSON REMOVABLE FROM THE UNITED STATES. Clearly, being in the US illegally "makes the person removable". The new law signed today (HB 2162) says A law enforcement official or agency of this state or a county, city, town or other political subdivision of this state may not consider race, color or national origin in implementing the requirements of this subsection except to the extent permitted by the United States or Arizona Constitution. A person is presumed to not be an alien who is unlawfully present in the United States if the person provides to the law enforcement officer or agency any of the following:
1. A valid Arizona driver license.
2. A valid Arizona nonoperating identification license.
3. A valid tribal enrollment card or other form of tribal identification.
4. If the entity requires proof of legal presence in the United States before issuance, any valid United States federal, state or local government issued identification. (my underlining)

Perhaps a step in the right direction - I suppose it gets the olive complected, dark haired people off the hook. However, SB 1070 seems to assume that anyone participating in informal street-corner labor pools is illegal, so I guess they are fair game.