It's terrifyingly awesome to start a MTB ride above the clouds, from the tip of a volcano, and on crushed pumice. Nothing really prepares you for that type of terrain. No matter the instructions, the photos you look at or the tales from other riders who have done it before you.
Ignoring the fact that you're 10K feet up and will ride through 10 of the world's 14 climate zones and you can see Mauna Lao in the distance, you have to fully focus on keeping the bike upright.
That's because the pumice you're riding on is not a stable surface.
You pedal, do NOT brake and pedal some more. Any movement with throw you which way the pumice decides. You can try this yourself, by purchasing a bulk quantity of pumice, tossing it onto the sidewalk and riding over it. What I resorted to was "hobby horsing" it. That's descending with the dropper seat post slammed down, both feet off the pedals as outriggers, and looking where you want to go, not down at the pumice.
Surviving the pumice section intact, we turned onto the singletrack and it was like the oldest old school singletrack you've ever ridden. Just one line twisting down off the mountain into of all things, a pine forest. We took a break there for a bit, then down some more, with rocks and roots. The ride wasn't that technical, just tight and always changing as the climate zones do. It's a ride that after a few runs you'd master, but for the first go, we took it easy.
The pads I was wearing indicated with deep scars that many before me did not.
Adding to the excitement was the goat carcass we rode through. And, then the big finish on a dirt and the paved road out of the Kula Forest to the lavender farm.
For West Coast roadies, and those that travel even farther, riding up and down Haleakala on the road is a rite of passage. I can confirm, it's even more awesome on dirt with downhill bikes.