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If / when you take a more or less direct route from Rapid City to Vegas:
Zion National Park in extreme southern Utah is along your route, and would be a wonderful place to shoot a human. . There are so many varied and dramatic geologic formations and vistas!
People complain about the extreme crowding at Zion, but you needn't let that be a problem; just park in the small roadside turnouts where nobody else is parked and access the backcountry on foot. . The only places you have crowding are the facilities and the established trails. . Walk off-trail, across the backcountry, and you will find loads of great areas for photography and no other people.
If you search for images of Zion, most of what you find will be these landscape photos shot from grand vistas. . But there are many more places in Zion that are much more conducive to photographing a model; more intimate little canyons and draws and rocky formations that are off the beaten path and would allow for some really creative photographic opportunities. . I mean, you could get REALLY creative there and shoot a lot of images that are very different than what you see anyone else shooting. . The topography is so steep in many places that if you want sun you just shoot on the sunny side of a formation, and if you want shade you shoot on the shaded side.
There is a campground with tent sites just outside the East Entrance of the Zion, called Hi Road Campground. . It's somewhere in the neighborhood of $40 / night to tent camp, which includes use of the shower and bath house. . This is quite expensive for a tent site, but it will likely be the ONLY place to go anywhere for many miles, short of the $150+/night motel rooms in the town at the Southern Entrance.
Another place that is kinda along your route is Hovenweep, just on the Utah side of the Colorado / Utah border:
https://www.nationalparks.org …venweep-national-monument
The place is so cool! . It features ancient Anasazi stone ruins that you can walk around and photograph. . There is also tent camping there, as well as a Visitor Center. . The neat thing about Hovenweep is that you will almost feel like you have the place to yourself. . I went on Labor Day weekend last fall, and there were very few other people there.
There is no lodging nearby, so if you want to stay in a motel, you'll probably need to stay in Cortez, CO, which is a little less than an hour away. . But motels in Chaves are very reasonable, so it shouldn't be much of a problem.
If / when you take a very circuitous western route from Rapid City to vegas:
The Columbia Gorge, along Interstate 84, which runs east to west along the Washington / Oregon border, is a place that may interest you.
There are many waterfalls, particularly on the Oregon side of the river. . Because the slopes are facing north on the Oregon side, you will have the shade you are looking for almost all day long in many places.
https://www.google.com …bih=718&biw=1336&safe=off
The Washington side of the river has drier habitat, because the slopes face south. . But there are still worthwhile points of interest, particularly Beacon Rock:
https://www.google.com …oECBcQBA&biw=1336&bih=718
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