Volcanic steam pushes up through the rock to release calcium which forms travertine and the terraces. The process is on going and this scene changes daily. The dark colored stripes are made by "thermophiles" heat loving organisms.
The bison move quite close to the vehicles in Yellowstone, despite that, much respect has to be accorded to them. The American Bison or buffalo has made a come back but they are limited to certain areas of the national parks, when their herds grow too large human tolerance for them is very limited.