The Koll Co. and Aetna Life and...

The Koll Co. and Aetna Life and Casualty Co. have sold the remaining undeveloped acreage plus five finished buildings in their jointly developed Carlsbad Research Center business park in Carlsbad to a real estate subsidiary of Union Pacific Corp. for $57 million.

Union Pacific Realty Co.’s purchase includes roughly 285 acres of developable land in the park located northwest of Palomar Airport Road at El Camino Real, plus 117,000 square feet of building space. The park now includes 1 million square feet of completed buildings, a figure that will grow to 5 million square feet once the park is built out.

Major occupants of the park include a Farmers Group regional headquarters office and a Chrysler Corp. automobile design unit. Koll acquired the 560-acre business park site in 1980 from San Diego Gas & Electric Co., Koll Vice President Mike Dunigan said Wednesday.

Union Pacific Realty, an Omaha, Neb.-based subsidiary of the holding company best known for its Union Pacific railroad unit, owns commercial real estate projects totaling approximately 1 million acres in 22 states, the company said. The Carlsbad project is UPR’s first project in San Diego County.

E. W. Christman, UPR’s Southern California region vice president, said the Carlsbad project could be the start of further investments in San Diego.

Among UPR’s major California holdings is the 600-acre Vintage Industrial Park near the interchange of Interstates 15 and 10 in Ontario, which upon completion will total 9.5 million square feet of buildings. The company also owns 500 acres of raw industrial land in Riverside and two industrial projects totaling 290 acres in Fontana, according to UPR project manager Peter Folkins in Ontario.

Based in Newport Beach, Koll owns 25 million square feet of real estate properties in the Western United States. Koll and various partners own several major San Diego projects, including the 385,000-square-foot Wells Fargo Bank building and the 330,000-square-foot Coast Federal Savings building.