The causeway you are looking at was built when I-80 was being constructed. Its purpose was to carry fill from the island for freeway construction. There was actually a belt carrier that brought materials from Antelope Island to the construction site along that causeway. Now, as to the color change, it certainly would need to be another change in mineral content. There isn't much water added to the lake at the south end, and so the salinity must increase. The red color doesn't come from the minerals, but rather from a couple of species of algae and bacteria present in the water that thrive on the high salt content. That's my guess, anyway. BTW, Robert Smithson chose the location for the Spiral Jetty because of the wine red color of the water in the north arm. On Monday, February 24, 2014 11:49 PM, Wiggins Patrick <paw@getbeehive.net> wrote: Some here will remember Brent's EPOD from a couple of years back showing the difference between the north and south arms of the GSL caused by the railroad causeway. http://epod.usra.edu/blog/2012/09/great-salt-lake-causeway.html (north to the left) I was reminded of that earlier today (yesterday if you are reading this Tuesday) when I saw something similar. http://users.wirelessbeehive.com/~paw/temp/GSL-1.JPG (railroad causeway on left, causeway described below on the right, in both north is to the left) But the thing is, I was over the south arm, quite near I-80 with Stansbury Island in the distance. It would appear the causeway-like structure in the south end is causing the same thing to happen. So going north to south we now go from blue water to green water, then fades back to blue and one more change to green. My first thought was that his "other" causeway was put there by those that mine minerals from the GSL. http://epod.usra.edu/blog/2012/08/evaporation-ponds-near-great-salt-lake.htm... But as Brent described in his EPOD the water on the south side of the causeway is lower in minerals. To quote the King of Siam, "Is a puzzlement" (here played by a Vladimir Putin look-alike http://vimeo.com/45346724). Another view of the south end color change looking south toward Stansbury Island and the Tooele Valley. http://users.wirelessbeehive.com/~paw/temp/GSL-2.JPG patrick _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options".