It's not just the size of the project that has many people in the rural community worried. It's where the water will come from for the casino and all of the hotel rooms.
"You could not have possibly picked a worse spot in the entire county of Sonoma," says HR Downs, who is with the OWL Foundation, an advocate for water resource protection.
"The casino is about the size of, [from] what we've seen projected, about the size of seven Costco's. It's over 760,000 square feet," says Downs.
Downs is worried about what will happen when thousands of visitors to the casino and resort turn on the tap. The underground aquifer below the casino site is one of the key sources of water for the city of Rohnert Park and some of the surrounding communities. In fact, there are already signs that growth in the area is straining the water supply.
A European research team studying the Rodgers Creek fault discovered Rohnert Park is sinking. A satellite image measures the "creep" or movement in the fault -- the red area on the image is where the Earth is sinking 13 millimeters a year.
"That's because of over-pumping of the ground water," says Downs.
"It's impossible to mitigate this environmental disaster," says Pastor Chip Worthington.
Worthington is among those who worry the casino may pump Rohnert Park dry, and in the process, destroy a delicate eco-system.
"There are five species right now, plants and animals that are on the site. They're endangered. So we are opposed to this because it's an environmental and a social disaster," says Pastor Worthington.
Not to mention the site is prone to flooding, as seen in a video provided to ABC7 by opponents of the casino.
There's also a history of water fights in the area. Lawsuits have questioned the validity of city-sponsored studies and found flaws in the data.
All those concerns have people scratching their heads wondering -- just what is Rohnert Park thinking?
City engineer Darrin Jenkins says ground water is only one of the sources of water in the city. He's confident there's enough water to go around.
"Based on the size of the casino project that they've identified, that's similar to the size we considered in our study, there is really no concern about there not being enough water," says Jenkins.
The Graton Rancheria has purchased more than 300 acres just outside Rohnert Park. They are currently working with the federal government to make it tribal land. That would make the site part of the Indian nation, protected from federal regulations. And in California there is no regulation of groundwater. Anyone can take whatever they're able to take.
The city says an agreement has been worked out with the leaders of the Graton Rancheria outlining that the tribe will act responsibly.
"I think the stance of the Federated Indians have been that they want to make a positive impact on the community. They understand that the project does have impacts but it does understand they do have an obligation to mitigate those," says Steve Donoley, Rohnert Park city manager.
Tribal chairman Greg Sarris declined our request for an on-camera interview but told us by phone: "We're a sovereign nation. We didn't have to make an agreement with Rohnert Park. Obviously water is a huge issue. We are going to do whatever it takes to use a minimal amount of water."
Sarris also told ABC7 any talk about water usage was premature because environmental reviews were still ongoing.
A key question in those environmental reviews: Is there enough water to go around?
Ultimately all of Sonoma County may have a say in the casino debate. There is currently a proposal before the Sonoma County Board of Supervisors to ask the community if they want the development of more casinos. That referendum is being considered for the November ballot.
Written and produced by Ken Miguel.
