The closure is pretty vast, but is only partly marked out in the field. For instance, the west side of Pacifico is quite clearly signed as closed, but if you go in from the east (Chilao) there are no signs. They probably just hadn't gotten to putting up signs because Mendenhall is relatively low-traffic.
BTW, Hwy CA-2 is still closed between La Canada and Red Box, so getting to Chilao is a big painus-a-la-anus. Hafta go lower Big TJ -> Ang For Hwy -> upper Big TJ -> CA-2, which makes for about a 2-hour drive from my current locale. Since Wrightwood (and east San G's) is about the same drive time (and a bunch better!) I've been doing that instead.