Marc S. Hendrix

The Geology Underfoot in …. series is intended as a supplement to the Roadside Geology of … series; while Roadside Geology… covers places that you see driving past, Geology Underfoot… covers destinations – you’re going there specifically to investigate geology - where you are expected to get out of your car and walk around a little. Not walk around a lot; almost all the stops in Geology Underfoot in Yellowstone Country are just roadside pull-offs (there are a couple of longer hikes suggested, usually to get an overall view of some area). As such, this format is more suited to geological features that need to be examined close up – rock textures, fossils, and so on – plus large scale features that are subtle enough to need more careful examination than can be done out a car window at 75mph. (My favorite in the series so far is Geology Underfoot in Illinois. A hypothetical “Roadside Geology of Illinois” would consist mostly of descriptions like “….and there are Devonian deposits under 300 feet of glacial drift below the soybean field on your left” while Geology Underfoot in Illinois takes you to the few places in the state where you can actually see bedrock, plus lots of subtle glacial geology features that require some observational time to figure out).


The stops are presented in chronological order – and since this is “Yellowstone Country”, not just Yellowstone National Park, many of them are outside the park boundaries. Since this is a large area – the park is bigger than several eastern states – if you go to every suggested stop you’ll end up spending most of your time driving. Not that driving in Yellowstone is intrinsically a bad thing, but the roads are narrow and the traffic heavy in the tourist season.


Author Marc Hendrix is a University of Montana professor specializing in mountain building processes; as might be expected, then, the primary focus is on the tectonic and structural geology of the Yellowstone area. Nothing at all wrong with that; this is a World Heritage site primarily because of tectonic and structural geology. The sedimentology and paleontology are a little weak – not objectionably so; however there are a couple of misleading statements. Hendrix describes brachiopods as “bivalves” which is correct in a morphological sense but not in a taxonomic one; and the discussion of turbidites makes it seem like they are only the result of storm surges (The event that led to the discovery of turbidity currents was the 1929 Grand Banks earthquake, and earthquakes are still believed to be a major source of turbidites in the sedimentary record). The real problem with the discussion of turbidity currents is the adjacent photograph, in which the turbidites are identified as “flood deposits”, which is not correct at all.


Hendrix also goes out of his way to warn readers that rock, mineral and fossil collecting is not allowed in National Forests without a permit. AFAIK this isn’t true; “recreational” collecting of “small amounts” (usually defined as 10 pounds) of rocks or minerals has always been allowed. There are designated areas that are off limits, only surface collecting is allowed (no digging) and vertebrate fossils are permit-only. This has been a contentious area – especially the “surface collecting” only rules. The problem is prospecting is allowed in National Forests under various mining rules – and a number of mineral collectors caught digging have claimed (with various degrees of success) that they were “prospecting” instead of “mineral collecting”. I emailed Shoshone National Forest (never got a reply) to see if they have any particular rules; I suppose I could always claim I’m a professional geologist and ask for a permit. Not much in the way of unusual fossils in the Yellowstone area anyway, although there’s some nice petrified wood. (Needless to say, there is NO collecting of ANYTHING in the National Park, as opposed to the surrounding National Forests, without a permit).


All in all pretty useful within the above limitations. I would not recommend it for a first time visit to Yellowstone, even to interested amateur geologists; the main reason is that you would spend too much time driving from one outcrop to another and not enough actually seeing all the iconic sights in the park. But for a second or third trip, or a series of trips specializing in particular geology (hydrothermal, glacial, etc.) it’s fine.… (meer)

At first glance, this looked to me like a cheap spinoff of the well-known Roadside Geology series. I own several volumes of the latter, but these do not, alas, include Idaho, Wyoming or (at the moment) Yellowstone. I picked up the Geology Underfoot volume at my local library and discovered that, as a book to read in the comfort of your living room, it is far superior to any of the Roadside Geology volumes I own. However, as an actual roadside guide, it probably has some disadvantages relative to the older series.

The difference is organization. The Roadside Geology series is just that. Each volume is organized as a set of road logs, explaining interesting geology in the order you would encounter it while driving down the road. (Unless you are going the other way, in which case you are like T.H.H. White's Merlin trying to live backwards in time.) The road log organization has obvious advantages while actually on the road and is the reason for the success of the series. However, it means you will tend to jump around the geological history of the area you are traveling in. The Roadside Geology series typically tries to get around this problem by providing an introductory chapter presenting the geological history of the area in a more chronological fashion.

The Yellowstone volume of Geology Underfood is entirely chronological, presenting a set of (usually closely clustered) stops for each important epoch in the geological history of Yellowstone. Thus, the first "vignette" takes you to the Great Unconformity between early Precambrian and the first Cambrian formations near Cody, some distance east of the actual Yellowstone border. (Note to Set: We gotta make this particular stop this summer. There are practically no Cambrian outcropping mapped in New Mexico.) Succeeding vignettes cover subsequent periods of geological time, with the final vignette taking you to the fault scarp of the big 1958 Yellowstone earthquake. The explanations of the geology seem excellent and the photographs and maps are quite good.

In fairness, it may be that Yellowstone, with lots of geology in a relatively small area, lends itself to this treatment. I also have a Geology Underfoot volume for Utah, and my quick impression is that it is organized a little more in the road log style. Regardless, I really like Geology Underfoot in Yellowstone.… (meer)