Among Hawaii’s great drives, Saddle Road—the Daniel K. Inouye Highway/Route 200—crosses the broad, barren pass between Mauna Kea and Mauna Loa: the Humuula Saddle. Those mighty shield volcanoes are not only Hawaii’s biggest, but also the two tallest mountains in the world measured from base to summit. The scenery and geologic riches abound along Saddle Road, and Puu Huluhulu is one of the standout stops. A short loop hike on its shoulders is definitely worth 45 minutes of your time!
Situated at the 28-mile point on Saddle Road, right by the intersection with Mauna Loa Observatory Road, Puu Huluhulu looms just south of the highway. It’s a mostly forested, 200-foot-tall cinder cone produced by eruptive activity associated with Mauna Kea. Embodying this frontier zone between mighty fire mountains, though, Puu Huluhulu comes surrounded by relatively young Mauna Loa lava flows.
Puu Huluhulu translates to “hairy hill.” That’s a reference to its forest cover, which stands in stark contrast to the bleak surrounding lava lands. Of course, when Puu Huluhulu first formed as a spewed-out pile of cinders, it itself was bare. But over millennia, its volcanic rubble weathered to soil and came to support vegetation. That was predominantly koa forest, which then also surrounded the cinder cone. Mauna Loa lava flows, namely major eruptions in 1843 and 1935, destroyed the surrounding forest, while the trees atop the cinder cone survived.
The result—the “hairy hill” of Puu Huluhulu rising above lava-flow expanses—is an example of a kipuka. This Hawaiian word describes an island of vegetation encircled by younger lava formations. Kipukas are not only evocative places but also ecologically precious: They serve as a seed source to naturally revegetate the adjoining lava “wastes.”
The cinder cone’s woodland— Kipuka Puu Huluhulu—preserves an ecosystem once more widespread in the vicinity, plus birds and other wildlife dependent on it. Decades ago, Puu Huluhulu was fenced off to prevent ravaging by feral pigs and goats. Now a Native Tree Sanctuary, it’s a delightful place to explore for the botanically and birding-inclined. And its unique position on the Humuula Saddle translates to some whopping views.
A hunter check-in station keys you into the Puu Huluhulu trailhead. You’ll enter the preserve through a gate in that pig- and goat-proof fence. We hope this goes without saying: Be sure to close the gate behind you!
The cinder cone’s short trail system creates a roughly 1.1-mile loop, with side trails and cutoffs giving you a few options for different routes. There are about 200 feet of elevation gain involved between the trailhead and the summit, which stands at 6,758 feet above sea level. All in all, it’s a fairly easy walkabout, though during or just after rainfall it can be slick in places.
Mostly you’ll be wandering koa woodland, with a plethora of other native trees and shrubs (as well as some exotics) present. The northwestern shoulder of Puu Huluhulu was quarried in the past, though, so it’s more of a barren geologic display. The birdlife ranges from native forest birds such as awakihi and apapane to the io (Hawaiian hawk) and nene (Hawaiian goose).
Various vantages on Puu Huluhulu’s flanks as well as the summit itself provide amazing sightlines over the Saddle and to its bordering volcanoes. Besides the giant profiles of Mauna Loa and Mauna Kea, you’ll have fine prospects of the 1935 lava flows surrounding the kipuka as well as other cinder cones studding this highland.
Puu Huluhulu is well worth the stop. If nothing else, it’s a great excuse to stretch your eggs on Saddle Road—and to adjust to the altitude, if you’re headed higher yet to Mauna Kea. But the geology, ecology, and long-range views on offer at this sanctuary are very much their own rewards as well.
-Near the northwestern foot of the cinder cone, look for the remains of a 19th-century stone wall, built by ranchers and partly swamped by the 1935 Mauna Loa lava flows.
-It’s a good idea to wear bright-colored clothing, as—despite its status as a protected reserve—Kipuka Puu Huluhulu is open seasonally to bird-hunting.