The following picture is the pic which was photographed by Melissa Dowland: https://twitter.com/m_dowland
Her scientific profile is: https://naturalsciences.org/staff/melissa-dowland
This picture was available on this webpage: http://naturalsciences.org/search#stq=%22Yellowstone+Lake%22+%22black+mud%22&stp=1
The rights of this pic was reserved, and maybe still reserved, for her & this ^ website
But, on the 3rd day of the year 2018 I noticed that the pic was removed from this ^ link
But, here you are: https://web.archive.org/web/20170629063423/http://sites.naturalsciences.org/education/Yellowstone/2005/pages/grizzly%20track%20in%20sand%20along%20Yellowstone%20Lake.html
This ^ link is saying that this pic is the pic of the black mud alongside the Yellowstone Lake in Wyoming state
So, I show you now the pic over here temporarily until I find an alternative scientific link showing the same pic or another similar pic
I took this ^ pic from this link: https://lh3.googleusercontent.com/99ouTWiho7o-- K1ocpQTvg5o1Z_gFCz9SFaUNbfookfmGTW013SctosJYw564C7w9xmSBw=s114
More info is available here: http://justpaste.it/zy