How to Experience Being Surrounded by Millions of Butterflies on Lassen Peak

Lassen Peak is known to many as Northern California’s most active volcano, having erupted just over 100 years ago. The mountain, which sits as the centerpiece for Lassen Volcanic National Park, is also one of the premier hikes in the area and can get you to nearly 11,000 feet elevation with just a moderate hike.

And if you time your hike to the top of Lassen just right, you can stand atop the massive volcano surrounded by millions of butterflies.

During the summer months, millions of California Tortoiseshell Butterflies undertake a seasonal migration — often traveling north to the higher elevations of the Klamaths, Sierra Nevada, and the Cascades. Their larva feed almost exclusively on species of Ceanothus and occasionally massive population booms can occur, resulting in near-epic numbers in migratory groups and making an amazing viewing party for hikers.

This migration typically hits the area between the months of late-summer/early-fall, with the high-elevation terrain of Lassen Peak being the perfect place to sit smack-dab in the middle of the butterflies.

While biologists do their best to track the migrations, they can be different every year. That means the exact date and size of the group of butterflies vary from year to year, but can last for weeks on end. Many scientists and news organizations track the migration, which can also be seen throughout the Tahoe area and even as far west as San Francisco’s Golden Gate Park. But Lassen Peak has seen the thickest and most consistent patterns over the past decade, with the butterflies whizzing past heads at speeds of over 25 mph.

To see these butterflies in person, you’ll need follow the migration patterns and be ready to head up to Lassen once they arrive. You’ll typically begin to see them in early-to-late July, with the sightings lasting possibly through August, although every year is different. We will report as soon as the migration enters the Lassen area, but for now you can enjoy the migrations from years past:

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