I went into the archives looking for rock photos and found these...
WIKIPEDIA says- The Saint Croix National Scenic Riverway is a system of riverways located in Minnesota and Wisconsin. It protects 252 miles of river, including the Namekagon River and the St. Croix River, and adjacent land along the rivers.
I took these photos while on a river boat ride at Taylor's Falls, Minnesota, and some of these rocks might qualify as boulders for 
The St. Croix is a beautiful river and the boat ride was a great way to see this section of water.
It is a great place to spend a summer afternoon!
@erikah
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