We entered Yellowstone's north entrance early in the morning, after camping outside (one last night of free camping before paying the big bucks at a campground). We stopped at the visitor center and made breakfast at the picnic tables as a herd of elk hung out in the sun not far away (a fella with huge antlers and a few of his lady friends and some young'uns). The rangers put up orange cones so people wouldn't get too close (even though there are signs everywhere saying to stay away, elk can be aggressive, they even had a continuous video loop in the visitor center of elk attacking people and cars).
We walked the trails around Mammoth Hot Springs which is almost like a foreign planet with all the mineral deposits making the land all white.
In the afternoon we drove out Lamar Valley and saw Bison and prong horn antelope... and also the smoke from a fire in the park that had been burning for a few days already.
We filled up with some bad Diesel in Bozeman Montana which wasn't apparent until after we'd been in the park for a day. We had troubles climbing the hills and ended up camping on a side road (a big no-no says the ranger who knocked on the window in the middle of the night). We limped over to a gas station early the next morning and Steve emptied the fuel into the jerry cans, filled up with new diesel and after chugging for a bit, it started running like normal (Steve was happy that worked because he was afraid the new motor was shot).
We crossed the continental divide again on the way to the Upper Geyser Basin where we saw Old Faithful go off a couple times, once from the benches around it, once from the trail that goes around to about 20 other geysers, ponds and springs in the same area. There is such a variety of bubbling, hot, acidic, water/earth activity going on. We saw Castel Geyser go off too, it lasted about 20 minutes! And apparently only blows about every 14 hours, so we considered ourselves lucky to see it.
We camped on Yellowstone Lake where we could hear elk bugling almost constantly, it sounds like a synthesized elephant call, must have been mating season.
We came across a herd of bison in the middle of the road on the way to the upper and lower falls on the Yellowstone River. They weren't in any hurry to get out of the way, to the dismay of a FedEx driver coming the opposite direction. They walked so close we could have reached out and pet them.