Is there any snow up there to melt any more?
When I was up there a month ago, there was still snow in the canyon above switchback 27 (though it could be 29 or 31). That is where the trail heads west for a ways and transitions over to the cliff face that includes the cables (if you look at Wayne Pyle's map). The lower part of that canyon faces north and is somewhat protected from the sun.
Exactly what I was referring to, in my semi sarcasm, responding to speculations such as that the water can come "from anywhere n the Sierra" and that the mountain is a big sponge with cavities and chambers and such. I am pretty sure that SB23 is just the emergence of the runoff from immediately above it from relatively short run at very shallow depth. As I recall, the inlet stream at Trail Camp is similar, in that it emerges (from a moraine?) a short distance up hill from that pond. I suspect that most springs in the Sierra are like this, as soil is shallow to non-existent and bedrock is solid.
Notable exceptions would be hot springs, such as at Kern and MTR, and some cold springs such as possibly the Outpost Camp spring.
Nothing mysterious about SB23: pretty sure its direct runoff from the north facing features directly above it.
