I was recently searching for an online overview of all Geology of the US and got that link to the USGS mapview which is quite amazing. This interactive tool serves as a national archive for high-quality, standardized geologic maps created by the U.S. Geological Survey and state geological surveys. The Snake River Plain, beneath that long flat stretch of Interstate 84, is covered by Quaternary age basalt flows. Aerial view of meander loops on Mississippi River, Louisiana. Here’s Rule #0: white areas, being mostly alluvium, mark low areas; colorful areas indicate bedrock, so are typically higher in elevation. Touring the geologic map of the United States, https://pubs.er.usgs.gov/publication/70136641, http://mapapps.bgs.ac.uk/geologyofbritain/home.html. The photo of Death Valley region as tilted fault blocks coincides with the inset on the cross-section. All rights reserved. It’s a very low angle fault so displays a very irregular trace as it winds in and out of the valleys, kind of like a contour line. And just beyond the Snake River Plain to the northeast, you can see Yellowstone, marked by rhyolites that also cover the older, surrounding rocks. Eugene’s in the center of the map . These rocks include intrusive igneous, undifferentiated metamorphic, and flat-lying sedimentary rock. The beauty of this map is that you can see the whole country at once, and using just a few rules, can immediately glean the underlying structure of a region. It excludes Alaska and Hawaii. The Ogallala Formation (yellow swatch), only about 6-2 million years old and up to 1000 feet in thickness, covers more than 170,000 square miles of the Great Plains –and provides drinking and irrigation water to the vast majority of people in the region. Aerial view of incised meanders of the Green River cutting through flat-lying rock, Utah. Terrific post! A geological map of Britain and Northern Ireland is freely available at http://mapapps.bgs.ac.uk/geologyofbritain/home.html. Geologic Time Scale. Compare it to the ribbon-like bands to the north and south, mostly steeply inclined, folded, and faulted sedimentary rock of the Fold-Thrust Belt. Copyright © 2020. In fact, the outcrop widths of vertically dipping beds equals their thickness! Map 3. It’s of about the same age and origin as the Sierra Nevada in California. Map 1. This one can be expanded to street level, and clicking on a location will give you a description of the bedrock, and the surface geology. The swatches mark approximately flat-lying sedimentary rocks and many of the ribbon-like edges mark monoclines, where the rock flexes from flat-lying to steeply dipping to flat-lying again, like the photo below of the San Rafael Swell. Key. Geologic map and and photo of the Grand Canyon, AZ. The U.S. Geological Survey hosts the National Geologic Map Database (NGMDB). This post is just an introduction, so I’ll stick to the boxed areas to illustrate some geological relations –and maybe throw in a few photos along the way. Hi Marli, longtime reader, first time poster. Yes– you really do need to have the legend nearby to consult –it helps with so many of the details! I am new to your site and just wanted to say how much I am enjoying it. This inset of a close-up of the Valley and Ridge shows a classic example of the zig-zag pattern that results from plunging folds. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. It has a search function that accesses more than 3500 images I’ve taken over more than 35 years. Aerial view of the southern San Rafael Swell, Utah. Click here to access the interactive database. It excludes Alaska and Hawaii. You can see that the rocks get younger out from the core if you click on the image to see it at full size. All rights reserved. Eugene’s in the center of the map. Click here to access the USGS's Geologic Map of U.S. States. Lewis Thrust, which lies just above the tree line, places Proterozoic rock over Cretaceous rock.
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