Groundbreaking work was to start Monday at the site of the planned casino just outside Rohnert Park, said the Sonoma County tribe behind the project.
The grading "signals the start of the nearly 900 construction jobs that will be created by the tribe's project," said a statement by Federated Indians of Graton Rancheria.
Unanswered questions remained Monday morning about whether the work was starting ahead of required approvals.
The tribe's 254-acre Wilfred Avenue property is exempt from virtually all local and state regulations, but official statements and documents have indicated there are steps that the tribe agreed to that must be completed before groundbreaking.
Neither tribal nor county officials immediately returned calls seeking comment Monday. Station Casinos, the Las Vegas-based corporation bankrolling the project, declined comment.