I assume you'll be in the Sierras, or the Whites. Typically at those elevations September is pretty mild (relative to location and elevation). However. The Sierra's often have local storms. I've seen days in the 80's and a couple hours later it's snowing. Granted, it Typically doesn't snow much, but the cold temps can stick around overnight. If I were you I'd look at Zenbivy and the many options they have. But, whoever you go with, take note of how they rate their bag/quilt. Most companies use a survival rating, some use a comfort rating, some use both. You want the comfort rating appropriate for expected temps in the area you'll be. If it's colder, layer clothing appropriately. But keep in mind that your clothing needs to allow heat to escape into the bag, (you may want the help that process a bit), after all, your bag/quilt and pad are what you're relying on, ultimately. Lastly, get an appropriately rated pad along with appropriate length and width (22 inch wide pads don't cut it. For me it's a long wide)
