NEW YORK—New York-based Square Mile Capital Management LLC has originated a $68 million mezzanine loan on a 31-property, 4.5-million-sq.-ft. office portfolio in Southern California, which was made to an ownership group that includes The Blackstone Group LP and a venture led by SL Green Realty Corp.

Financial terms were not disclosed.

SL Green assumed ownership of the portfolio in lieu of foreclosure in July, and then recapitalized the portfolio by forming a joint venture with Blackstone. Proceeds of the mezzanine loan are being used to recapitalize the portfolio as part of New York Life Insurance Company, Dekabank Deutsche Girozentrale, Münchener Hypothekenbank EG, Westdeutsche Immobilienbank AG and Wells Fargo’s extension and modification of the $678.8 million senior financing on the portfolio.

Comprised of 59 buildings, the portfolio’s properties are located in Los Angeles, Orange County and San Diego submarkets. Some of the assets include the LA Corporate Center in LA North, Skyview Center in the LAX submarket, 350 S. Beverly Drive in Beverly Hills and Carmel Valley Center in San Diego’s Del Mar Heights.

In partnership with USAA Real Estate Company, Square Mile originated and structured the loan, which is the firm’s inaugural investment in the mezzanine origination marketplace.