Central O'ahu, being slightly more removed from the hustle and bustle of downtown, is a great place to head for some quieter hiking along serene trails, and Wahiawa Hills offers a diverse array of ecosystems over a 4-mile loop trail. Being located in the Ewa Forest Reserve, permits are required for entry. The trails are not well-marked, and many people have gotten lost trying to follow the loop, making this a rather difficult hike on top of its rather untamed nature. The trail also lives up to its name, with only 500 feet of elevation difference between the highest and lowest points on the trail, but it sends hikers on an undulating journey gaining over 2000 feet in total along the steep hillsides. The continuous ups and downs are a real workout, with the final ridge ascent being dubbed Cardiac Hill. The pleasant river crossings and pools offer a serene reward at multiple points along the trail, although be careful after heavy rains.
The trail starts at the end of a quiet neighborhood on California Avenue in Wahiawa, past the two water towers, and descends quickly down a rooted ridge to the left. Follow the base of the valley along a small stream. At a crossing just below a small waterfall, the trail begins to re-ascend the other side of the valley using a couple of switchbacks. Fallen trees require some navigating, and soon an indiscriminate junction is reached, marking the start of the loop section. A small pig trail heads down to the left. A slight right follows the contours of the ridge and is the correct way to start. Notice the trail coming from above, down the ridge directly to the right (this is the return leg of the loop). Follow the contoured trail that makes its way to yet another junction. This time take a left down to the first crossing of the Kaukonahua Stream. This wide, yet shallow river can swell with current after a large rainfall, but either way, expect your shoes to get soggy!
Across the stream the trail ascends the ridge and is sure to get the blood pumping. At the top of this broad ridge, burned trees can be seen from a large forest fire that spread through the area. Along the ridge, hikers will continue climbing and descending hills, passing a dirt road heading back toward Wahiawa as well as a rain catchment container. A couple of openings in the trees afford views of the surrounding valleys, the Ewa Forest Reserve, and the distant Ko'olau summits. The trail begins to bank to the right before dropping steeply again to the valley floor. Push through dense clumps of ferns and grass to make it to the second river crossing of Kaukonahua. A quick dip in the cool water provides the perfect relief before climbing the steep and exposed ridge on the other side. At the top of the ridge the trail becomes more gradual, meandering through tall grass, native 'ohia, and koa trees. The final mile begins the descent back to the junction above the river. Aromatic lemon eucalyptus trees fill the air with a scent reminiscent of pine and citronella. Bank a hard left to return down the switchbacks, ducking below the moss-covered fallen trees, and crossing the same small stream below the waterfall. The hike concludes with the final climb up Cardiac Hill and past the water towers to the road.