A group of Silicon Valley billionaires led by former Goldman Sachs Group Inc. trader Jan Sramek have quietly bought up over $800 million worth of Northern California farmland to create a new city from scratch. But their vision of a sustainable utopia is drawing persistent opposition from locals who are fighting to preserve a rural way of life.

At the first of several town halls meant to win over the community, Sramek laid out his vision of turning the land into a dense, walkable city that would create high-paying jobs and boost economic growth. But many residents at an event late Wednesday were outraged by his proposal, shouting him down as a “shill” and “smooth talker” and leveling allegations that his company, Flannery Associates LLC, engineered a secretive land grab.