Tres Hermanos Ranch

Tres Hermanos Rancho Grand Avenue

The cities of Diamond Bar and Chino Hills are deeply concerned about the apparent plans by City of Industry to build a massive solar farm on the 2,450-acre property known as Tres Hermanos Ranch.

Latest Information

December 10, 2018 - The City of Commerce continues its attempt to acquire Tres Hermanos Ranch out from under the City of Industry. The Los Angeles County District 1 Oversight Board meeting on Monday morning December 10, 2018 considered an agenda item to approve the sale of the Tres Hermanos Ranch to the City of Commerce.  Diamond Bar, along with representatives from the cities of Chino Hills and Industry were at the meeting to present written comments and testimony indicating objections to the item. The Oversight Board ultimately tabled the matter until they could obtain independent legal counsel to review and advise them on the proposed transaction.

November 26, 2018 - In an unprecedented attempt, City of Commerce has made a bid to acquire Tres Hermanos Ranch out from under City of Industry. City of Diamond Bar became aware of Commerce’s efforts with the posting of a public agenda for the Los Angeles County District 1 Oversight Board meeting with an agenda item approving the sale of the Tres Hermanos Ranch to City of Commerce. The meeting originally scheduled for November 26, 2018 has since been cancelled. City of Diamond Bar responded with correspondence submitted to City of Commerce at its Closed Session meeting on November 20, 2018 indicating objections to the proposed purchase and reiterating Diamond Bar’s outstanding litigation with City of Industry regarding the property.

The City's Position

Diamond Bar City Council is strongly opposed to Industry’s plans to build a massive solar facility on the Tres Hermanos property. Compounding this concern is mounting evidence of flagrant and repeated violations, inconsistencies and contradictions on the part of the Successor Agency, the Oversight Board and the City of Industry with regard to actions taken in relation to the Tres Hermanos property and the proposed development.

Diamond Bar has filed several lawsuits to protect the interest of the City and its residents challenging the Oversight Board’s decision to approve the sale of Tres Hermanos Ranch to Industry, and the lease agreement between Industry and a private entity to develop a solar generating facility on the property.

City of Chino Hills has filed similar lawsuits.

Legal Action - Lawsuits filed by City of Diamond Bar include:

City of Diamond Bar vs City of Industry - First Amended Complaint, January 2018 (Sacramento County Superior Court) - Challenges the purchase of the Tres Hermanos property alleging that such purchase violates the State’s Redevelopment Dissolution Act (Originally filed in October 2017).

City of Diamond Bar vs City of Industry – November 2017 (Los Angeles County Superior Court) – Alleges that Industry violated the California Environmental Quality Act (CEQA) by attempting to purchase the property and entering into a lease for development of a solar facility without conducting any environmental review.  Also alleges failures by Industry to comply with State planning and open meeting laws.

City of Diamond Bar vs City of Industry – April 2018 (Los Angeles County Superior Court) – Alleges failures by Industry to produce public documents under the California Public Records Act related to the sale, lease and development plans of the Tres Hermanos property for a solar facility.

Tres Hermanos Aerial Site Map8-20-18

Download a PDF copy of this map or view an online version of this map.


Tres Hermanos Ranch is 2,450 acres of undeveloped open space located along the eastern edge of the city between Diamond Bar and Chino Hills. Approximately 730 acres, or 30 percent, of the property is within Diamond Bar; the remaining 1,720 acres are located in Chino Hills. The portion of land within Diamond Bar is located northerly of Grand Avenue and is visible from Diamond Ranch High School.


Tres Hermanos Ranch is currently held in trust by the Successor Agency to the Industry Urban Development Agency on behalf of all the taxing entities, which include the cities of Diamond Bar and Chino Hills, and the County of Los Angeles.

According to a City of Industry memorandum, this property was owned by the City of Industry but transferred to the former Industry Urban Development Agency in the late 1970s. 

Under the Redevelopment Dissolution Act of 2011, the Oversight Board is charged with and has a fiduciary responsibility to maximize the value of the property for the benefit of various taxing entities, which includes Diamond Bar, Chino Hills, and other public agencies.

At its meeting of August 24, 2017, the Oversight Board approved the Successor’s Agency’s sale of the Tres Hermanos property to the City of Industry for $41.65 million.

Proposed Use

For over two years now, the cities of Diamond Bar and Chino Hills have been diligently working to find out what Industry has in store for this property.  In October 2017, Industry’s City Manager stated in writing that the City does not have any definitive plans for the future use of Tres Hermanos, however, an agenda item before the Industry City Council at that same time sought to ratify a Master Ground Lease and four amendments for a 450 megawatt solar generating facility on the property.  More recent media articles (July 2018) have suggested that the solar project is no longer being pursued according to Industry officials.  The City will remain engaged and continue to take appropriate steps to determine Industry’s intentions for the property.

Misinformation & Misconceptions

Existing Land Use Designation

Falsehoods and exaggerations have been circulating regarding the number of housing units permitted on the Diamond Bar portion of the Tres Hermanos property. Under the current Diamond Bar General Plan, only 30 of the 730 acres within Diamond Bar’s jurisdiction is designated high density residential and would allow up to 490 attached units. The remaining 700 acres are zoned either agriculture or very low density and would allow up to 140 single family detached units – which is one residence per five acres.  

Phone Poll

Several individuals have reported receiving calls from an organization conducting a survey that appeared to be aimed at gauging knowledge and opinion, and even influencing support for the development of the solar project on the Tres Hermanos property. According to the reports, the narrative provided and questions asked as part of this poll were clearly biased and misleading.