Refer to Hikin Jim’s CalTopo (He listed it in his reply to the High Creek post about a month ago) rather than the Tom Harrison in this case. Tom Harrison has misplaced Mineshaft Flats camp – it is a little further away from Mineshaft Saddle and the Cal Topo has a better location for the camp. The water back there is in the Northfork creek mentioned above just a short distance from the camp. We don’t get a lot of trail reports from back there, but the general outlook I have gotten from over the past 7 years is that the water runs fairly reliable until sometime around mid to late summer. If you plan to go there after the end of July, you will want to know about other water sources in case you need them. Again the CalTopo does a good job of indicating the creek locations, but you’ll want to reach out to this forum (or SGWA or SocalHikers Facebook groups) again for any updates that we or other hikers can give you.
You can get to Mineshaft Flats either by way of the Fish Creek trail to Fish Creek Saddle, then to Mineshaft Saddle and then down the Mineshaft/Big Tree trail, OR you can get there via South Fork to Dry Lake and take the route through Trail Flats to Mineshaft Saddle and so forth.
Nearby water at Lodgepole Spring should be reliable until the end of summer. Fish Creek (near Fish Creek camp) should be OK until the end of summer.
Hope that helps.