BTW, the diagonal highway is nice (SH200)! It is new and we were one of the few cars on it.
Our observation...
The whole west side of the Island was mostly lava fields (except around Kona). The airport is surrounded by rolling lava fields for miles and miles. King Kamehameha's “birth place” (north west) is all lava fields.
The North and East are lush and green. This is contrast to all of Maui was is mostly lush and I imagine Kauai is even more lush than Maui.
It was explained to me that it is because the Big Island is newer and hasn't had the millenia for the forests to fill in and the weather to wear down the rocky lava terrain.
The couple on Buying Hawaii bought a place north of South Point. It was in the high risk lava plane. There wasn't any water or electricity and it was in a very rocky lava field. They paid around $250K for it.
You can buy a freshly built house on 1 acre in Hawaiian Paradise Park for $250k WITH electricity etc. and it is quite a ways from the lava fields. Whatever tv show you were watching.....they got hosed.