This is a loop that starts and finishes at the Koke'e State Park headquarters. From the parking area head south across the grass to a grassy trail that heads up the hill to Highway 550. Cross Highway 250 and head along Kumuwela Road. This is a dirt road. Be aware that there will likely be cars on this road. There are lots of beautiful wildflowers along this road, so enjoy.
At about eight-tenths of a mile in, you will want to head off to the right on Mohihi Road, another dirt road with vehicle traffic. Mohihi Road heads straight to the Berry Flats Trail. There is a trailhead marker on the left side of Mohihi Road. If you have a handheld GPS, the trailhead is at N22? 07.848 W159? 38.327.
The Berry Flat Trail is not very long and since this description does not include the entire length of the Berry Flat Trail, you'll only travel seven-tenths of a mile until you'll connect with the Water Tank Trail. While the Berry Flat Trail is short on in distance, it more than makes up for it by being long on scenery. There is a rich green to the whole area. There are abundant redwoods (yes, redwoods), which are obviously not indigenous, but beautiful nonetheless.
Once on the Water Tank there is one substantial difference that you'll notice compared to the Berry Flat Trail. You will start seeing an abundance of a plant with a flower that looks like a yellow lantern. This plant is called Kahili Ginger. This is an invasive weed and the state of Hawaii is fighting a losing battle to eradicate it. Interestingly, until recently, Hawaiians loved this flower because of how fragrant it is. It was used in ornamental gardens.
As the trail continues on you'll pass a number of trees that have some very unusual root structures. When I say unusual I mean above ground unusual. In fact, one of these trees straddles the trail forcing you to walk under the roots. I'm 6' 3" tall and I didn't even have to duck to walk under these roots.
Eventually, the Water Tank Trail will end at a dirt road that will take you straight to Highway 550. From here you will have to walk southwest down highway 550 until you get back to the State Park Headquarters. Note that Highway 550 is pretty busy and is narrow without much of a shoulder. So be careful.
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.