I've replaced my June 3 image with one of the same spider in better light/focus. This was taken around 10:30 AM in my front hedge. I've also revised my size estimate down from approx. 15 to approx. 12 mm. Thanks to Jeff's and Sasha's photos, I finally figured this one out. (This dorsal shot showed leg tufts that I couldn't see in the ventral shot.)

I guess the blobs are a practice stabilimentum as it learns its weaving skills. Also, its web has a 3D depth to it, more like a chamber than a wheel. When inadvertently disturbed as I tried to get a good position, it set up a pretty impressive vibration for a few seconds, then calmed down.