Road tripping to National Parks

So for two weeks, I found myself in the US. In the southwestern part of the US, specifically; Arizona, Utah, Nevada (and some New Mexico and Colorado thrown in at Four Corners).
How did I end up there? A friend of mine had a conference in DC, and we decided to do some road tripping afterwards. Genuine road tripping, that is, no plans or reservations or anything, just driving around and seeing where we'd end up. So we had a place of arrival and departure (Phoenix Sky Harbour airport, although we arrived and departed separately due to financial reasons) and a rental car, and that was basically it. We'd go wherever the road would take us.
Turns out, it took us to National Parks. Loads and loads of National Parks. On the third day, some friendly ranger told us that we could actually buy an Annual Park Pass for just 80$, which would save us entrance fees to most National Parks (except for those on Navajo land, as they can still charge), and after that, we were really unstoppable.
There is so much beautiful nature in that part of the world. Vast stretches of empty nothingness, with very few roads or villages in between. We drove the length of our own country several times over, and saw nothing but nature with a capital N (okay, and some flattened prairedogs, coyotes, etc. But most of it was alive and not on the road). And it's so diverse! You can be driving through a flowering cactus filled desert one minute, and stand at the edge of a pine forest-filled canyon the next. I've done the middle of Australia, and that has a lot of nothing too, but it's mostly the same red-orangy desert nothing. Here, you never knew what to expect in the next 100 miles.
If we would have been a bit better prepared, we could have done some very nice long hikes, but as things were, 35+ is just too many degrees to start trumping about unprepared. We did some really nice and rewarding short hikes to arches and canyons and the tops of volcanoes, and otherwise saw the rest of it from the ideally located view points (in the beginning, we'd take pictures from the road, but then we found out that if ever there was a nice few, there would be a scenic view point for us to get out and snap away as we liked).
So, any favourites? Of course! If you're in for petrified forests (and believe me, you are), go to Petrified Forest National Park, and take the scenic drive past thousand year old trees (no collecting, or you'll be cursed forever). If you're into arches and other weirdly shaped rocks and geographical features, go to Arches National Park (see what they did there? Even if you're completely unprepared, the name of the park will just tell you what to expect. And in the park itself, you had stuff like 'sheep rock'; a rock shaped like a sheep, 'balanced rock'; a rock balanced on top of a thin spire, and 'delicate arch'; a... you get the gist by now). Visit Bryce or Zion National Parks for the best hiking in slightly lower temperatures. And of course Monument Valley, where I managed not to wreck our rental car on the 'dirt' (=gravel) roads.
All in all, we drove 4500 kilometres. We did not venture into California, as it has too many great things to fit in just two weeks, and decided that we'll have to come back for that some other time. Probably a bit earlier in the season, as the tourist crowds really started to get going towards the end. But still, two weeks of being so totally removed from your own 'habitat', under the vast blue skies and the big empty roads; I wouldn't mind coming back next year!