This is a good picture of the rocks - but Tristan looks a little grumpy 

Tristan, Cecilia, Violet and Sam enjoy some time with Ronald during the rain delay at HayMarket Park. 

and another pic 

On a trip to Trenton, we stopped at Fort Kearny. Here is Tristan in front of a cannon. 

And Cecilia 

Here is Tristan - King of the world 

This gives you a better idea of the size of the rocks. 

Another picture, It was fun to climb on the rocks. 

Outside of Minneapolis, KS is a place called Rock City. It has a number of these "secretions".