Thanks, BP. I am in upstate NY. Not sure if we have goatheads here... The guy at my LBS said it may have been a rock that slowly worked it's way in and caused a slow leak... I was riding on chip seal or something like that and there was some loose stuff on the shoulder. But who knows it could have been a thorn too--I only got a quick glimpse of it without my glasses before losing it.

I am trying to stay away from the shoulder when it's safe. Will try immersing the tube to locate the puncture... Thanks for your input!