Terri Cook

Mountain Press of Missoula, Montana publishes two geology series: Roadside Geology of… and Geology Underfoot in …. The first covers geology as seen from major highways, assuming that the user is on the way to someplace and, while curious about what’s seen out the windows, is interested in further examination. The second is still based around auto travel, but now assumes that the reader is going to specific places with the intent of examining the geology. (There’s another series, Hiking …’s Geology, which is published by The Mountaineers Books, and is geared toward fairly serious backcountry hikers). Geology Underfoot Along Colorado’s Front Range is the most recent of the Underfoot series (published November 2012) and is very well done; I’ve been to most of the places mentioned in the text (although usually have not explored them in the detail provided by the authors).


For a book directed at lay people, this is very much up to date, incorporating some new work that I wasn’t familiar with (specifically discussion of the “Mid-Tertiary Ignimbrite Flare-Up”). There are numerous color illustrations; some are pretty pictures of rock outcrops but may are isometric or cross section drawings that excellently supplement text explanations of the geology; I was particularly impressed by the discussion of the multiple pediment surfaces visible around Boulder and Rocky Flats, and the use of North Table Mountain, South Table Mountain, and Green Mountain near Golden to illustrate the Tertiary Rocky Mountain Erosional Surface. The authors also discuss multiple working hypotheses for some geological features – for example, is the Pike’s Peak Batholith a remnant of an old mantle plume or related to the Rio Grande Rift?


I have some minor quibbles. The sites in the book are presented from north (State Line kimberlites) to south (Trinidad Lake KT Boundary clays) rather than in geochronological order. Since each chapter is stand alone, this requires authors Lon Abbot and Terri Cook to explain some things several times – particularly the Yavapai Orogeny. In turn, that means each explanation is less thorough than it could be and some illustrations seem out of place. The authors also seem a little weak on ore genesis and mining technology (I should stress I’m not necessarily up-to-date on these things myself, so the apparent fault may be with me). In the chapter on the Cripple Creek mining district it’s implied that gold concentration is a result of magmatic rather than hydrothermal processes; in the chapter on Idaho Springs it’s stated that the yellow color of old mine tailings is due to sulfur compounds (AFAIK it’s from hydrated iron oxides) and that the purpose of smelting is to “melt” ore (it’s to reduce it – i.e., deoxidize it).


There are no end notes or footnotes, but each chapter has its own reference list. The references seem a little sparse, and I’m surprised Roadside Geology of Colorado isn’t mentioned, despite being from the same publisher. Nevertheless this is an excellent book and I plan on working my way through a lot of the trips mentioned.… (mehr)