Jakob Dylan of The Wallflowers, actress Daryl Hannah and others ended the rally Tuesday by singing "Stand By Me" on stage together at Civic Center Park.

Co-organizer Allison Wolff says the budget for the Frack Free Colorado event was about $45,000. The rally was meant to push for the acceleration of clean-energy alternatives and to educate the public on what Wolff calls the dangers of hydraulic fracturing, which involves blasting water, sand and chemicals underground to free oil and natural gas.

The research arm of the Independent Petroleum Association of America counters that fracking is safe and that both Republicans and Democrats have said U.S. natural gas production supports jobs and the nation's energy security.

(Copyright 2012 by The Associated Press. All Rights Reserved.)