Scott,
I should have said EPSG:3857 and EPSG:900913 above though in my limited understanding they are different terms for the same projection.
TMS subscription?? I see Caltopo supports WMTS and KML if that helps. Is TMS also what Gaia GPS is using? I noted that it's not WMS and that's why I went looking for alternative WMS access (already a Gaia subscriber). The point of this exercise, besides learning and gaining access to more tiles, is to get a land management layer that includes AZ State Trust land.
Looking at my network traffic for downloads, I see that several of the Topofusion maps appear to be using something other than standard WMS. I bet this also explains why MyTopo/OpenCycleMap etc. don't show up in the tile download window, right?
I would appreciate the flexibility to use other projections and/or a more flexible interface to servers though I can understand how that might turn into a can of worms.
I'll contact you by mail with more info that can't be shared publicly.
Ben