The lower 48's first dozen established NPs:
1872: Yellowstone (Wyoming)
1890: Sequioa (California)
1890: Yosemite (California)
1899: Mount Rainier (Washington)
1902: Crater Lake (Oregon)
1903: Wind Cave (South Dakota)
1906: Mesa Verde (Colorado)
1910: Glacier (Montana)
1915: Rocky Mountain (Colorado)
1916: Lassen Volcanic (California)
1919: Grand Canyon (Arizona)
1919: Acadia (Maine)
The last dozen:
1994: Death Valley (California)
1994: Joshua Tree (California)
1994: Saguaro (Arizona)
1999: Black Canyon (Colorado)
2000: Cuyahoga (Ohio)
2003: Congaree (South Carolina)
2004: Great Sand Dunes (Colorado)
2013: Pinnacles (California)
2018: Gateway Arch (Missouri)
2019: White Sands (New Mexico)
2019: Indiana Dunes (Indiana)
2020: Three Gorges (West Virginia)
Death Valley is a GOAT contender as far as I'm concerned, with GOAT level night skies for galaxy gazing; the lowest elevation on the continent 282 feet below sea level and hottest location on earth, arguably the most extreme place on the entire planet. It's got badlands, canyons, craters, sand dunes, salt flats, hills, strenuous hiking trails, mountains, lookout points, and peaks galore. It was stupidly stuck on national monument status since 1933 for whatever reasons.
And then Congress should've stopped there with its establishment on Halloween 1994. California and Colorado did not need an additional two NPs a piece beyond that; the real Three Gorges is in China, breh; Oh, "new river gorges", yeah whatever. The Indiana Dunes sit next to a fucking power plant and steel mill; the Congo thing is an average floodplain. And hell, why not designate the longest standing McDonalds arches in the country a National Park while they're at it? Very American.