I do not know where you are leaving from or how much money you are budgeting for this trip. People tell me that gasoline is expensive now. I know if you are going somewhere for the first time driving should be avoided altogether.
When you drive an automobile you have an obligation and responsibility, of course,to drive with care. Sightseeing can never take priority over safety, so naturally much will be missed by the driver. It is not easy at all to enjoy cities and landscapes from behind the wheel.
Flying gets you places fairly quickly, and while you are not required to pilot the aircraft your only access to the areas you are moving through is an uncomorftable aerie some thirty thousand feet in the air.
My strong suggestion is that you ar least look into the railroad.
This will not only provide you with a relaxed sightseeing sojourn, but your aunt, who seems to have a strong emotional tie to the West, will be traveling into the land like so many did for over one-hundred years.
You will not need to search for gasoline in an unfamiliar place, will not need to look for and pay for parking.
Believe me, someone who has crossed this continent many times in various ways, the West, like most of the Earth, is too pretty and at times too stunningly fantastic to be stuck behind the wheel of an out-dated, air-fouling, negative form of transport.
Train travel is the most affordable and enjoyable mode of
exploration. You will roll mile after mile, looking out upon plains, forests, deserts, prairies, canyons, hills, rivers, falls, and the world's great ocean, the Pacific.
On the train you can get up and stretch and walk around. The large, reclining seats are fine for sleeping. In many places the rails do not roll through the same corridors as the highway so you are afforded incredible vistas that drivers and air travelers never see.
Not knowing where your trip originates, the West coast is accessable across the North by the Lakeshore Limited,which connects from New York and New England. From there the Empire Builder goes through the Northern plains and Montana's Glacier Park to Seattle and Portland. One can reach from the Pacific Northwest to SanDiego, nearly the entire US West Coast, via the Coast Starlight.
An alternative is the Southwest Chief swings Southwest through the heartland to the Rockies, and then down through the Raton Pass into New Mexico and West through Arizona to Los Angeles.
The California Zephyr reaches San Francisco from Chicago via Denver and Salt Lake City.
If you are heading West from the Southeast the Sunset Limited runs from Florida to Souther California.
There are so many places to visit that it would require a book to describe, but I personally would suggest Los Angeles, San Francisco, and Portland. I particularly enjoy visiting new cities, but certainly Yosemite Valley, Death Valley, the Rockies, the spectacular sculptured rock look of the Southwest, and the Pacific Coast are not to be missed.
Taking the train will provide you with a lifetime of scenic memories and you will arrive home in a much more relaxed state than if you were to drive. Have fun!!