Visited in Fall of 2016. No caretakers, no guards, a few benitoite miners more concerned about their rocks. Fire has taken out most of the area not immediately around the rotary furnace.
Regarding mercury, I wouldn't really worry about it too much. If you are, don't go there.
For my periodic science lectures on Health and UrbEx, here it goes:
There are three types of the heavy metal poisoning. The deadliest is inhaling mercury vapor, which tends to lead to almost immediate, chronic and possibly fatal nerve, lung and brain damage. However mercury vapor is volatile (hence why it is inhaled) and is more than likely to evaporate within a few years of production. Suffice to say don't go kicking open any glass or metal canisters and this shouldn't be an issue.
Far more likely is ingesting mercury, likely organically through say fish living in the area. Due to the fact that mercury accumulates in the body, eating contaminated fish will expose you to a lot of mercury, leading to GI damage, nerve damage and the works. The most famous heavy mercury poisoning case had to do with eating contaminated fish: https://en.wikiped...i/Minamata_disease
Do not eat the fish.
Finally, there are inorganic mercury compounds, probably from the environment. Inorganic mercury will be everywhere at a site like New Idria: the dirt, metal objects, etc. You will likely be contaminated-probably through inhaling the inorganic mercury, which can eventually lead to the same damages as above. However the damage will likely be minor/limited if you visit only a short period of time-similar to coal, asbestos and radiation, it's mainly chronic, repeated exposures that generally lead to problems here. Definitely change clothes after exploring/before eating and don't do it too often, due to the fact that as I mentioned above, it tends to stay and accumulate in the body.
However New Almaden in San Jose is another mercury-contaminated site, and it is very popular with joggers and families, if that gives you some reassurance.
Wear a mask if you decide to visit the buildings of New Idria, though that is more important for small dust particulates, black mold, hantavirus, asbestos etc. than mercury. http://www.calpois.../callusvol9no1.htmhttps://yosemite.e...0001900463#threats