Today's march headed toward the state capitol

The Republic estimates the crowd at 10,000:

The throng of people banged drums, chanted slogans asking President Barack Obama to intervene and waived American flags as they made their way toward downtown Phoenix. Organizers were scattered throughout the protesters picking up trash and providing water to the marchers as the day got progressively hotter.

Shortly before 12:30 p.m., the first of the protesters reached the Capitol after the long march from central Phoenix. A stage is set up in the middle of the Capitol complex where speakers will address the crowd in a post-march rally.

Arizona Capitol Times is covering the march, too, but ups the crowd-size estimates considerably:

Tens of thousands of protesters, composed of activist groups and unions from around the country, marched from Indian Steele Park in mid-town Phoenix on their way to the state Capitol May 29, trying to send a message to state and federal politicians: Repeal Arizona’s new immigration law.