The Golden State Warriors delivered forward Harrison Barnes an initial four-year, $64 million contract extension proposal, league sources told Yahoo Sports.

Harrison Barnes (Getty Images) More

The $16 million annual offer wasn’t accepted, but appears to be a starting point in talks that could last until the Oct. 31 deadline for rookie extensions.

The Warriors are trying to prevent Barnes from reaching restricted free agency in July 2016, when a rising salary cap and scores of teams with financial flexibility will couple with Barnes' burgeoning talent and potential to make him a significant target on the market.

As a member of the 2012 NBA draft class, Barnes is eligible for his rookie contract extension. Without an agreement by Oct. 31, Barnes would become a restricted free agent next summer. Golden State would be able to match any offer sheet for Barnes and re-sign him.

The offer of $16 million per year annually – comparable to teammate Draymond Green's five-year, $82.5 million extension this summer – had been negotiated by Barnes' former agent, Jeff Wechsler. After that initial offer, Wechsler countered with a figure north of $16 million annually before he and Barnes parted ways, league sources said. Jeff Schwartz of Excel Sports is representing Barnes now.

Under coach Steve Kerr, Barnes started to blossom amid the Warriors' deep roster of talent during their championship season. Barnes, 23, averaged 10.1 points and 5.5 rebounds last season, and graded out as one of the league's most efficient players.