Sleeping Bag Question.

Depends if you sleep hot or cold, are comfortable boosting with clothing taken along, are in a tent or bivy, the R-rating on your pad, and how high you are going in spring and fall. A conservatively rated 30F bag (WM, the Sierra Designs Nitro, maybe Marmot Hydrogen) will work if augmented with a puffy layer and you're using a pad with maybe a 5+ R-rating. A 15F bag is maybe a little safer choice, but likely too warm in mid-summer.

15 or 20 degree rated (what most people find comfortable a bit warmer) down bag with full zip is ideal for the Sierra 6 months of the year. Weight can be under 2 pounds. I find that down bags of the same temp rating have a wider comfort range than synthetic. Full-zip (to the beginning of the footbox, not around the bottom) lets you use it as a quilt in warmer weather.

If you will be spending more time in So-Cal than the Sierra, and most time midsummer rather than May or October, going with a 25-30 rating might make sense to you… But I've seen 5 degrees in early October so I'd stick with the lower rating.

You could save a pound by going lighter (higher temp rated), less zipper, lighter materials, and/or a quilt. You might find need for a second bag though. If it's your first backpacking bag I suggest a moderately priced, moderate weight down bag and then learn from your experiences using it before spending several hundred on a top quality item.

I'm fairly happy with my REI Sub-Kilo 15 that I "stole" for $83 on double-clearance sale last year. The current REI Halo 25 is similar and probably more accurately rated.

ty for the info, im on the right track :)