Half Dome, Yosemite National Park. May 1995. Sadly, I've only visited Yosemite once, and then only for a couple days (I was on my way back to Yellowstone and had a deadline). And it rained most of the time I was there, so I didn't do much hiking, although I did get in a few miles on my then-brand new bicycle. So Yosemite is something I may need to do again sometime, even though weekdays in May were still too crowded for my tastes.
Yosemite is occasionally billed as the first national park, an argument which is partly true, but is also incorrect in an important way. There's no question about its priority over Yellowstone as a protected area. Upon pleas from prominent local citizens, the federal government withdrew the Yosemite valley from settlement in 1864 and gave the land to the state of California*, on the condition that it be managed as a public park and protected from resource extraction. When Congress set aside Yellowstone eight years later, the park proponents made direct reference to the Yosemite Grant as a precedent, and even the language of the act itself mirrored the text of the earlier grant.
But Yosemite was not a national park; it was a state park. No doubt Yellowstone would have been made a state park, too - if there had been a state to grant it to. As it turned out, Yellowstone lay mainly in the northwest corner of Wyoming Territory, which in 1872 consisted primarily of a string of towns stretched along the Union Pacific Railroad far to the south. It was going to be many years before there would even be a state government, let alone a state government with a presence in the Yellowstone region. So a national park it had to be - "The National Park" was its official name - and a national park it remained When Wyoming achieved statehood in 1890, the enabling act explicitly excluded Yellowstone.
With the meadows were being overgrazed and the Giant Sequoias heavily logged, Yosemite needed more protection, at least in the minds of conservationists such as John Muir and the magazine editor Robert Underwood Johnson. They publicized their disapproval and successfully spurred Congress to action. This time, instead of giving more land to California, the government created a new national park surrounding the valley in 1890, with a troop of US Army cavalry to run the show. Yosemite was now imitating Yellowstone, which had remained under federal control and, when it required more supervision and protection, had been placed under the control of the Army just four years earlier. When the National Park Service was established in 1916, the circle was completed: the state park was ceded back to the federal government** and the present-day Yosemite National Park came into being.
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* A good example of how the states never automatically owned all the land within their borders, as some fools erroneously claim.
** In this case, giving up land was a good deal for the state. The federal government pays the bills, the local economy gains the tourist dollars, a formula which probably goes a long way in explaining the eagerness for national parks. The formula only failed when the locals didn't want any park at all.