Let me clarify a bit about the forests and closure orders. The TLDR is in bold below.
In general, in the USA, public land is kept accessible to the people as an important basic right and freedom. There are only a handful of closures that are common, and they are generally limited to specific areas and often apply only to vehicle access, for example when roads are soft and muddy and vehicles would cause damage. In that kind of a situation people would be allowed to be there on foot.
Or, when there is human activity that is dangerous to be around -- whether that is fire fighting or timber cutting, the specific area and the roads leading to it may be closed to anyone not involved in the activity. Again, limited to only the affected area.
I don't believe public land would close to keep people safe from normal risks of storms etc -- people are allowed to choose to be in risky situations -- but for something unknown such as this Sierra NF trail-specific or river-specific closure, it makes sense to close access until they know what's going on.
But the thing about the regionwide closure of all forests in the state -- I have been a NF employee or former employee for nearly 30 years now, almost all of it in California, and I have never heard of that extensive a closure before.
Here's the thing -- this closure is NOT about the normal risk of fire -- forests can and do ban smoking, campfires, woodcutting (chainsaws often throw sparks), etc every year during times of high risk but they don't ban people from simply BEING in the forests.
What's going on now is this: there are so many fires currently going across the west that if new fires were to start -- the USFS HAS NO MORE FIREFIGHTING PERSONNEL AVAILABLE TO SEND. It's not even mostly about money, it's about all trained fire folks already maxxed out.
Fires most often start from lightning but obviously that can't be stopped. They are trying to eliminate the risk of any human-caused fires because it's all they can do to reduce fire needs right now.
I will look for a link to share but until I find one this is MOO.
Edit: Link to the USFS letter addressing the closure:
https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd949147.pdf