We started from the North. We were prepared for at least 5 miles thanks to AllTrails. We were also aware that there was no shade, so we had water, sunscreen, and long-sleeve shirts. The trail reminded us of the trail to Green Sand Beach on the Big Island.
You can park near the reserve, but you need a permit. I have the info so we can get a permit next time (it'll give me a reason to drive our Jeep Wrangler!). For those wanting the info:
www.hawaiistateparks.org, 808.587.0300. I presume when you get the permit, they give you the code for the lock on the gate. For those reading, don't do it unless you have a 4x4. Sedans will not suffice!