If you’ve ever driven the 57 Freeway through Tonner Canyon, you’ve seen it. It’s that massive, rolling expanse of green and gold that sits right where Orange and Los Angeles Counties collide. It looks like a postcard from old California. That is Los Tres Hermanos Ranch. Most people just see it as pretty scenery while they're stuck in traffic, but for the cities of Diamond Bar, Industry, and Chino Hills, this land has been the center of a decades-long chess match. We are talking about 2,445 acres of prime real estate. In Southern California, that much open space is basically a unicorn.
It's wild. You have this huge footprint of undeveloped hills surrounded by suburban sprawl. For years, the question wasn't just "What is it?" but "Who gets to control it?"
The Weird History of Los Tres Hermanos Ranch
To understand why people get so worked up over this dirt, you have to go back. Way back. The name itself—Los Tres Hermanos—translates to "The Three Brothers." It wasn't just a catchy brand. In the early 20th century, three heavy hitters in the Southern California power scene bought the land: William Chandless of the Los Angeles Times, Harry Chandler, and Moses Sherman. These guys basically built modern LA. They used the ranch as a private retreat. Imagine the kind of deals that were made over whiskey and steaks out there while the rest of the region was still orange groves.
Eventually, the City of Industry’s cattle company took over. Industry is a tiny city with hardly any residents but massive industrial wealth. They bought the ranch in the late 1970s. For a long time, the plan was to build a dam. A reservoir. Something to secure water rights. But that never happened. Instead, the ranch became a political football.
One day it’s a proposed solar farm. The next day, developers are drooling over the idea of thousands of luxury homes. Residents in Chino Hills and Diamond Bar? They hated all of it. They wanted the hills to stay hills. You can’t blame them. Once you pave over a canyon, it’s gone forever. There’s no "undo" button for a housing tract.
Why Everyone Fights Over These Canyons
Honestly, the tension comes down to a fundamental California problem: preservation versus profit. Industry owned the land, but the land sits mostly within the borders of Diamond Bar and Chino Hills. It’s a jurisdictional nightmare.
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- Diamond Bar and Chino Hills residents want to keep the "rural feel."
- Industry wanted to utilize the land for regional benefits (and let's be real, financial ones).
- Environmentalists want to protect the wildlife corridor for mountain lions and deer.
Around 2017, things got heated. Like, "lawsuits flying everywhere" heated. The City of Industry was looking at a massive solar project. It sounded green on paper, but the locals saw it as an industrial eyesore. The pushback was intense. It resulted in a massive legal settlement and the creation of the Los Tres Hermanos Conservation Authority. This was a huge win for the "keep it green" crowd. Basically, the three cities finally agreed to sit at the same table. They formed a joint powers authority to manage the land.
It’s rare to see three cities actually agree on anything this big. Usually, it's just endless bickering until a developer swoops in with enough cash to silence the critics. But here, the focus shifted toward open space and "passive" use.
What’s Actually Happening Out There Right Now?
If you try to go hiking there today, you might be disappointed. It’s not a public park yet. It’s still a working ranch in many ways, with cattle grazing to keep the fire risk down. That’s a common tactic in California—let the cows eat the fuel so the whole canyon doesn't go up in flames in August.
There is a lot of talk about "mitigation banking." This is a bit of a technical term, but it’s basically a way for developers elsewhere to pay to keep this land wild as a trade-off for building in other places. It’s a financial engine that keeps the ranch from being turned into a shopping mall.
The hills are rugged. The views are incredible. From the highest peaks on a clear day, you can see the San Bernardino Mountains and the Pacific Ocean. It’s a vital piece of the "Missing Linkages" project, which aims to keep natural paths open for animals moving between the Cleveland National Forest and the Chino Hills State Park. If you block off Los Tres Hermanos Ranch, you effectively trap wildlife in islands of habitat. That's how species go extinct locally.
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The Solar Controversy That Almost Changed Everything
We have to talk about the solar thing because it nearly broke the region. The City of Industry had this vision of 450 acres of solar panels. They argued it was necessary for renewable energy goals. The neighbors argued it would destroy the views and the soil.
The reality? It was probably a bit of both. But the backlash was a reminder that in 2026, "green energy" isn't a magic word that lets you do whatever you want with protected land. The settlement that stopped the solar farm is why the Conservation Authority exists today. It shifted the mission from "energy production" to "preservation."
The Future: Will You Ever Be Able to Hike It?
That is the million-dollar question. People in Diamond Bar are constantly asking when the trails will open. Right now, it’s a slow process. You have to deal with:
- Liability issues. (The terrain is steep and fire-prone).
- Infrastructure. (There are no real parking lots or bathrooms).
- Environmental sensitivity. (Too many hikers can actually ruin the habitat they're trying to save).
The Conservation Authority is working on a Master Plan. It’s not going to be a Disneyland-style park. Think more like "low impact." Maybe some managed trails, some educational spots, but mostly just... nothing. And in Southern California, "nothing" is a luxury.
Actionable Steps for Locals and Visitors
If you care about what happens to this massive chunk of California history, you can actually do something besides just staring at it from the 57.
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Monitor the Joint Powers Authority Meetings
The Los Tres Hermanos Conservation Authority meets regularly. These aren't exactly "must-see TV," but this is where the decisions about trails and land use are actually made. If you live in Chino Hills or Diamond Bar, these meetings affect your property value and your backyard.
Respect the Boundaries
Seriously, don't go trespassing. There are still active ranching operations and sensitive habitat areas. Getting caught out there doesn't just result in a fine; it hurts the argument for opening the land to the public. If people show they can't respect the rules now, the cities will be much slower to build those trailheads.
Support Local Land Trusts
Groups like the Puente-Chino Hills Land Conservation Authority have been instrumental in these fights. Following their newsletters is the best way to get a "heads up" when a new development proposal or a new trail plan hits the desk of a city planner.
Think About the Wildlife
When you’re driving through the area, especially at night on Grand Avenue or the 57, slow down. This is a high-traffic area for animals moving through the ranch. Coyotes, deer, and the occasional mountain lion use these corridors.
Los Tres Hermanos Ranch isn't just a big empty space. It’s a reminder of what the Inland Valley looked like before the concrete took over. It's a victory for local activism. It's a complicated, expensive, beautiful piece of land that proves sometimes, the best thing you can build is nothing at all. Keep an eye on the Master Plan updates over the next year—that's when we'll finally see if the gates get nudged open for the rest of us.