General Motors Co. and Dan Gilbert's Rock Ventures LLC are working to develop a swath of land, at least some of which GM owns, on the Detroit River totaling more than 20 acres just east of the Renaissance Center.

According to sources, the development of the area south of Jefferson Avenue would be mixed use, with a combination of multifamily units, retail and other uses.

Sources' accounts of the project status differ, with one source saying an architecture firm has been chosen and Gilbert's company selected to develop the land. Another source said negotiations between GM and Gilbert's team are ongoing.

"We do not comment on speculation or rumors," Carolyn Artman, senior public relations manager for Rock Ventures, said in an email this afternoon. "Any company business or other matters that we decide to disclose publicly will be done so through the proper channels at the appropriate time."

The exact boundaries of the property are not known, but it is believed to include property purchases GM made within the last 18 months.

GM in May 2014 purchased four properties — three vacant buildings and a surface parking lot — on the river, with one of the buildings, Schweizer's German restaurant, being demolished in December.

The buildings totaled almost 31,000 square feet and a 0.8-acre surface parking lot east of the RenCen.

The buildings — located at 673 Franklin St. between St. Antoine and Rivard streets, 672 Woodbridge St. between St. Antoine and Rivard, and 260 Schweizer Place between Woodbridge and Franklin — totaled almost 31,000 square feet.

A 0.8-acre surface parking lot at 689 Franklin St. is between St. Antoine and Schweizer Place.

It would be west of the $65 million first phase of the Orleans Landing development, which recently broke ground.

If the GM/Gilbert development comes to fruition, this would be the largest Detroit development site in which Gilbert, the founder and chairman of Detroit-based Quicken Loans Inc. and Rock Ventures, has been involved to date.

Bedrock is part of the development team on the $70 million Brush Park project, which is on an 8.4-acre section of the 100-acre plus neighborhood planned for more than 330 residential units and about 10,000 square feet of retail space. The riverfront site is at least 2½ times the size of that, in terms of acreage.

Rosko Development Co. LLC, which is registered to Howard Luckoff, one of Gilbert's childhood friends and closest confidants, has the development rights for a pair of two-acre sites downtown, the Monroe Block and the site of the former Hudson's department store on Woodward Avenue. Gilbert gained development rights to those sites when he decided to move Quicken, which was then based in Livonia, to downtown Detroit five years ago.

Another site, which eventually became the Z garage on Broadway Street, was also part of the package getting Quicken Loans to move its employees to the city's central business district.

The project would also mark Gilbert's first real estate venture south of Jefferson Avenue.

According to the most recent tally, Gilbert now owns more than 80 properties in and around downtown — totaling more than 13 million square feet with an investment exceeding $1.8 billion.

GM's plans to develop the area east of the RenCen go back at least a decade to around 2006, when the automaker tapped Chicago-based real estate companies Mesirow Stein Real Estate Inc. and Morningside Equities Group to develop a 13-acre property for the River East project into retail and residential space.

Those plans fell through because "we couldn't make economic sense of what GM and the city of Detroit were requiring … just the whole package of expectations regarding what would be built, who would build it, how it would get done, whether GM was going to be a partner, what they were demanding as their share of the development," David Strosberg, president of Morningside, said Wednesday. "So it just stopped making sense."

At the time, Matt Cullen, currently the president and CEO of Rock Ventures (and chairman of the Detroit RiverFront Conservancy board of directors), was the general manager of GM's Economic Development and Enterprise Services division.

"It's ironic," Strosberg said of Cullen's new role on the project.

The boundaries of the River East project were to be Franklin Street to the north, Rivard Street to the east, the Detroit River and RiverWalk to the south and Beaubien Street to the east.