The Battle Over the Tres Hermanos Ranch

  • Posted on 25 February 2019
  • By Robin Smith


One of the last important, large parcels of natural open space, located on the eastern border of Los Angeles and San Bernadino counties, has been embattled since the late 1970’s, when City of Industry purchased the land, under a cloud of scandal.  The historic, “Tres Hermanos Ranch” is 2,450 acres of freshwater emerging wetland, oak woodlands and savannah, forage land for golden eagles, and habitat for burrowing owls and cougars, connecting the Puente Chino Hills Wildlife Corridor and the Cleveland National Forest.  Situated between the cities of Diamond Bar, Chino Hills, Pomona and Brea, it is a stunning experience of open golden or green shades, a quintessential California native landscape, dotted by a small herd of grazing cattle, amidst choking urbanization.

Diamond Bar and Chino Hills share much of the natural resources within their cities because they were built within the attending hillsides and canyons, which lend a unique sense of character to the communities. Tres Hermanos is actually a contiguous part of both cities, as well as an important wildlife linkage to Puente Chino Hills.

Barely four miles from the San Gabriel Mountains, and aligning Puente Hills, Tres Hermanos Ranch is geographically: upper, mid and lower Tonner Canyon.

At least 6,000 acres of the entire area is owned by the infamous City of Industry.  Industry, is a “city” with less than 200 residents, dedicated to corporate, industrial and business enterprises.  Since its formation, the city has garnered a disreputable public image due to continual scandal. The book, “City of Industry” by Victor Valle, reliably captures the essence of Industry’s history, up to 2009. And since Industry purchased Tres Hermanos, worries of its proposed uses plagued the cities of Diamond Bar and Chino Hills, since final decisions were out of their hands.

The ongoing saga included (1) having Industry own the land alone; (2) whether San Gabriel Valley Water and Power should build a massive solar farm; and (3) having the oversight of all of that land be governed by the California Public Utilities Commission.

However, after a long, arduous and litigious journey of tracking the potential destiny of the land, all three cities, have resolved the lawsuits and come to an agreement, reforming a new joint powers agency: Tres Hermanos Conservation Authority.

The latest change moves the land use battle to the local level, where it belonged in the first place.

Since 2016, the Diamond Bar – Pomona Valley Sierra Club Task Force, has been participating in the current update of Diamond Bar’s General Plan as well as in the meetings of the Tres Hermanos Conservation Authority.  Many challenges still loom in attaining authentic conservation planning of natural open space in Diamond Bar and Chino Hills. Both cities currently have development zoning on Tres Hermanos, even though they claim to desire to save the land for “public and rational use”.  Actual land use designations will unfold and be deliberated in the forthcoming meetings of the Tres Hermanos Conservation Authority.

Readers may learn about the complex history and story of this special property located online via the Hills for Everyone website. They have a dedicated library to this topic. The Diamond Bar Sierra Club Task Force, prioritizes studies and civic participation for this and all local natural open spaces. The group continues to escort land use decisions in the area.

One impactful event, currently in process, is the designation of land use for Diamond Bar’s 700 acre portion of Tres Hermanos.  The DBPVSC task force is lobbying for conservation planning and an ecological-overlay zoning instead of the existing affordable-housing zoning.  A growing cadre of environmental non-profits and residents are emerging to weigh-in their vote to save the land, contiguously and entirely. Responsible Land Use, the Diamond Bar Preservation Foundation and the Facebook group called Save the Tres Hermanos Ranch, are watching over the entire process.  No one wants more housing or traffic.

With the new science of “natural green infrastructure” and recognizing the negative impacts which would occur if this particular property were to be squandered on housing or warehouses, the Sierra Club's task forces propose that the best use of the land is to save it contiguously, for future generations and the support of wildlife connectivity. Tres Hermanos, also known as Tonner Canyon, has been, and hopefully will remain, for the future, a legacy of California's natural landscape, for all.

Diamond Bar – Pomona Valley Sierra Club Task Force


Phone:  909-861-9920


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