Due to a rockslide just past the Mueller Tunnel, the dirt road leading toward Mt. Markham, Mt. Lowe, SG Peak, etc. is currently closed to foot traffic--at Eaton Saddle. However, plenty of hikers seemed to be ignoring this closure; the rockslide apparently does not block too much of the dirt road. Of course there may be an ongoing rockfall safety issue, and I'd guess that on weekends the rangers would seriously enforce this closure.
The closure is still in effect as of June 2011, but many people are ignoring it...risking a citation! The rockslide destroyed the fire road and part of the tunnel's west portal, but there is enough trail for a person to get across.