"This was so important, democracy does work, people do matter, it's wonderful," said quarry opponent Marelle Dorsey.
The quarry would have been a place to mine for aggregate, which is a material used in construction projects.
Supervisors who supported it said it would bring a number of benefits, including at least 100 new jobs.
"The benefits of this project to the community at large significantly outweigh any negative impact," said Riverside County supervisor John Benoit.
But supervisors who opposed the quarry said they had a number of concerns. In the end, the swing vote belonged to supervisor John Tavaglione.
"There are just too many uncertainties for me, I just can't support this project at this point," he said.
Quarry opponents were overjoyed.
"We worked so hard, all these people, and it affects all our lives, and I took a day off work, I didn't get paid to come here, and we're so happy," said Temecula resident Carol Buck.
Still, there are those who think the board made a bad decision.
"I just don't understand where the opposition is on this one, so I'm very disappointed, and I think the rest of us are outraged," said Alba Brizuela.
Karie Reuther of Granite Construction addressed the decision in a statement:
"Unfortunately, this region still faces a looming shortage of aggregate that will have to continue to be met by importing materials from distant sources. This is not a sustainable practice and will come at a growing cost to the region's traffic conditions, air quality and economy."
It is possible the quarry developer could challenge Thursday's decision with a lawsuit, but word yet as to whether that's going to happen.