A group of tech billionaires including Marc Andreessen, Reid Hoffman and Laurene Powell Jobs are buying land near San Francisco to build a self-contained utopia for the wealthy. They are funding a firm called Flannery Associates, which has purchased more than 55,000 of agricultural and unused land about 60 miles north of San Francisco. Flannery Associates purchased much of the land at above-market prices, leading to questions about the firm’s motives. As the company reaches out to local officials, its intentions are coming into focus.