Not every closure is a bad thing. I know – coming from me, that probably sounds surprising. But hear me out.
The San Dimas Experimental Forest, tucked into the hills north of Glendora in the Angeles National Forest, has been closed to public recreation since March 23, 2026 – and unlike some closures I could name, this one makes sense to me.
Here’s the deal. The San Dimas Experimental Forest isn’t a park. It isn’t a trail system. It’s a working outdoor laboratory that’s been quietly doing some of the most important long-term environmental research in California for decades. Climate studies, soil science, air pollution monitoring, erosion research, wildlife studies, fire behavior research – it’s all happening out there, with instruments and monitoring stations scattered across the landscape that need uninterrupted data to be worth anything.
You walk through the wrong drainage and kick over a sensor that’s been collecting data for fifteen years – that’s fifteen years of baseline data compromised. No dramatic explosion, no obvious damage. Just a gap in the record that can never be filled back in.
The closure order was executed March 23, 2026, by Dr. Frank H. McCormick, Acting Station Director for the Pacific Southwest Research Station, and it runs until further notice. It covers the entire San Dimas Experimental Forest as depicted in the official closure map. Exemptions are narrow – permitted researchers, government officials on duty, and organized rescue or firefighting personnel.
This is exactly the kind of public/private land management I believe in. The Forest Service is protecting a long-term investment in understanding how California’s landscapes actually work – the kind of foundational science that informs everything from watershed management to fire policy to species recovery. You don’t get that data by accident. You get it by protecting the conditions that make the research possible.
So if you’ve been eyeing the San Dimas area for a hike, find somewhere else for now. The work happening in there is worth more than the trail day you’d get out of it.
More info: Angeles National Forest – Experimental Forest