August is about the time Jumbo Rocks goes on reservation, there were many sites open when we went thru in July. Rock climbing season is when the place fills up.
Since it's still hot in August you can probably get a walk up site. The day of the week is a big factor as well: Monday - Thursday you chances are higher. Friday - Sunday it's more difficult.
When the park reopened from the shutdown, reservation signs are in every campground. Hence, I assume you still have to call in to inform them about your visit and that you are interested to reserve a spot
Not sure, this was my first visit!
Thanks! Your answer is awaiting moderation.