It would help if whenever someone passes on information like this, you could include a link to the agency involved or at least some authoritative source (other forums are not authoritative). We don't want to participate in spreading rumors and it would help to know the reason and if its temporary or permanent.
Gavilan Hills is in Riverside County and I would think the county ordinance against target shooting on public land probably supersedes the BLM. Besides, its developing pretty rapidly out there. Lots of homes on a few acres scattered all through there. Sprawl screws up everything. Whitewater Canyon has been closed for awhile I think - at least I've been told that. It's almost like a nature park in there. They bus kids up there to play in the river.
Info came from the BLM Palm Springs office. I emailed my contact there to ask if the places I go shooting where still open for shooting (Berdoo & Fergo Canyons) and also ask about an area I wanted to coyote hunt. He sent me the info I ask about, also the BLM notices and maps on the closed areas. the areas are closed temporary due to the high fire levels. Whitewater was open but one had to be 150 yds from any trails or buildings with a shotgun & 300 with a rifle and as you said not a safe place to hunt or shoot anyway. No time frame is listed as to when any of these areas will reopen. By the way at this time you also need a fire permit to even use a camp stove..