40 degree sleeping bag

[OldsRocket]

Would a 40 degree sleeping bag be sufficient in the San Jacintos and San Bernardino mountains for most of summer? How much colder are the primitive sites (Round Valley, Little Round Valley, etc) than Idyllwild? I know the elevation difference can be significant, but it appears that Idyllwild lows are in the 50s and 40s at night throughout much of summer. Big Bear seems to be similar. I want to get an affordable and light sleeping bag so if I can get a 40 degree bag instead of a 20 degree bag that would be nice.

I appreciate all advice.

[Sose]

Should be ok with an insulating ground cover or pad beneath it. Thermarest, buckskin or whatever. Remember, June and September nights can be chillier than July and August.

[Hikin_Jim]

I usually use a 32 degree bag, which isn't a whole lot warmer than a 40 degree bag. I'm thinking that 40 F should be fine for summer. However, as has been pointed out, "shoulder" season can be cold. The last couple of Memorial Day weekends, I've taken my daughter out, and it's been too cold for a 40F bag in my opinion.

And of course you need some kind of insulating pad as has been mentioned. Closed cell foam, self inflating open cell foam, air mattress designed to retain heat. I usually look for an "R" value of about 2.5 to 3.

HJ

[OldsRocket]

I am supposed to be going up for my overnight from Idyllwild to Round Valley in the next couple weeks. I know the weather forecast can change in that time but IF it stays the same (90 degree day 60 at night and no chance of rain) would I be a fool to leave thermal underwear and rain jacket behind?

Also, how much water would be recommended for the hike from Idyllwild to the ranger station by the tram. I'm planning 5 litres but I'm thinking that may be excessive. I'm hoping to start early 5 or 6 am to avoid hiking during the hottest part of the day.

Lastly, how easy is it to get lost at night on the trail from the peak back to Round Valley? If I get ambitious I may try to head to the peak to see the sunset after setting up camp and getting water from the ranger station. If I get lazy I will just hang out at the tram and enjoy the sunset over the Coachella Valley.