The culprit

I felt discomfort in my right shoe.  Took the shoe off and shook it out thinking there was a stone in it.  Discomfort still there when I put the shoe back on.  "I need to investigate further," I said to myself  (Aye, aye  'e'll be answerin'  'imself next) so off came the shoe again and this time I discovered a lump on the outside edge of the shoe; I looked and saw part of this stuck in the lining.  I had to push it out the way it came in.  A different angle nearer the middle of the heel (yes, this penetrated a rubber heel) and I really would have been in pain.  I wonder what kind of plant produces thorns like this?

       A few days ago I posted a blip of an old seed-drill at the historical park in Springerville.  I went back and snapped a few more angles in the sunshine this morning and have posted some of the results on Flickr.
Here's one with a little more context and taken from a lower angle as suggested by both Skeena and sdg92.  And a sepia tone of the original image..