Kalauao Gulch is a lightly used trail off of the extremely popular 'Aiea Loop, with no real signage marking any of the junctions. Thus, most hikers walk right by without even knowing it. Kalauao is unique compared to its more popular counterpart in that it boasts a picturesque waterfall and swimming hole when visited under the right conditions.
The trail starts at the 'Aiea Loop Trailhead in the Keaīwa Heiau State Recreation Area. Follow the beginning of the 'Aiea Loop for about a half-mile. Just after the second overlook clearing, a trail junction branches off to the left. Take this left turn down a tunnel of strawberry guava trees and along the adjacent ridge. Go under the power lines and continue on until reaching a large mango tree on the right, marked inconspicuously with spray paint and carvings. Head down the steep ridge trail to the riverbed below. Remember the junction with the river, as this will be the way back on the return leg. Following the river's edge upstream, the trail crosses the stream roughly nine times before reaching the falls. If the riverbed is dry, then chances are the waterfall won't be too spectacular, but it's still worth the journey. Be cautious if you'll be hiking after heavy rains, as this area is prone to flash flooding.
The falls can't be missed and rise roughly 30 feet from a tranquil pool of varying depth. A small trail ascends the falls to the left behind the massive banyan trees that flank the cliffs. The easiest return is to retrace the same path back up the ridge, ending at the 'Aiea Loop parking lot. Be on the lookout for plentiful strawberry guavas (Psidium cattleianum) along the trail during August and September as well as regular guavas (Psidium guajava) by the riverbed and ohi'a 'ai (mountain apples).
This 4-mile round-trip out-and-back trail is not overly strenuous, but it accomplishes most of its elevation gain in a steep half-mile section. Careful footing is required when navigating the down the steep ridge trail to the valley floor below. Plan to tackle this trail after a heavy rain or during the winter rainy season for the best chance of seeing the falls in action.