We hit Yellowstone at the end of May, 2006. We camped inside the park for the first couple of days. The weather was not our friend in Yellowstone. As we drove into higher elevations along the way, there was still snow on the side of the road. We wondered what we would encounter once we arrived at our destination.
It was a bit nippy. In fact, we had to run our taps overnight to make sure our RV water lines didn’t freeze. The next morning, we woke up to snow. A lot of the roads and paths were closed in the park due to the weather.
We made the best of it:

We enjoyed Old Faithful, and other geysers. The geysers of Yellowstone have a desolate beauty. That being said, there are plant species that grow and thrive in this location, including Ross’s Bentgrass, native to Yellowstone. Source: https://www.nps.gov/features/yell/ofvec/exhibits/ecology/plants/plants2.htm
Outside the geyser regions, the park is home to typical mountain region plant species such as evergreens and wildflowers. Animal life includes bison (many, many bison), bears, mountain goats, elk, and deer.
We moved camp due to the cold weather inside the park. In West Yellowstone, the weather vastly improved. We were able to enjoy our Yellowstone visit a lot more after the weather climbed about 10 degrees.
The town of West Yellowstone has a giant screen movie theatre which shows informative videos about the park, restaurants, accommodations, and other amenities.
We left West Yellowstone and concluded our Yellowstone National Park trip with my husband visiting Lewis and Clarke Caverns.
“Lewis & Clark Caverns State Park is Montana’s first and best-known state park featuring one of the most decorated limestone caverns in the Northwest. Naturally air conditioned, these spectacular caves lined with stalactites, stalagmites, columns, and helictites are electrically lighted and safe to visit. Above ground, a self-guided nature trail provides opportunities to understand the natural surroundings. ” Source and for more information: https://www.visitmt.com/listings/general/state-park/lewis-clark-caverns-state-park.html

Being slightly claustrophobic, crawling thru caverns and ducking down low to avoid the stalagmites and so forth was not my idea of a good time, so while he toured the caverns, I settled in at the nearby campground with a good book.
Parts of this trip truly showed how much camping is a fair weather sport!