Might be useful to some folks:
https://www.tripadvisor.com/Articles-lcs53ezkppi8-Dog_friendly_national_parks.html
Note: I suggest checking individual park websites before going, because they can change policies. And they’re often specific, like when we went to the Grand Canyon with our dog, they said dogs must stay above the rim.
Thank you so much for these websites. They are invaluable.
It’s also great to check entrance fees. If you (or your house owner) has a lifetime or annual pass for parks under the US Federal Government, you will save a lot of money on entrance fees. There are also state and local parks - again, check with the house owner to find out if they have an entry pass or parking pass.
On my checklist, I’ve made a note to ask owners if they have a blanket or covering for the backseat for when I take their dogs out and about, so that I don’t spend hours vacuuming my car.