Tunnel Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Red Loop)

I’ve worked in the oil & gas industry in Downtown Houston for over 15 years.  Like many others, every day I walk through tunnels on and surrounded by lovely rocks, minerals, and fossils without a second thought.  Though we may not have mountains in this part of the state, we have a stunning skyline and a tunnel system few people know about, and I will take these beauties for granted no more!  After the most recent Texas Parks and Wildlife Becoming an Outdoors Woman workshop that my friend and I teach geology for twice a year, the idea of creating a downtown walking tour sparked.  We enlisted a fellow geoscientist also located in Downtown Houston to join us in our quest.  We found a few scattered tours and information online (referenced below), an e-book on Amazon (link below), and little else.  So Katy, Christen, and I have set out twice a week to scout all of Downtown Houston on favorable days (preferably double digit temperatures) and tunnels during the summer months (or rainy days).

We’ve taken hundreds of pictures and have tried to find as many facts and best guesses as possible.  If you do one of our self-guided tours on your own and find more accurate information, we’d be happy to update it here.  We proudly bring to you the second of several self-guided walking tours: Red Loop, which is almost exactly the same rocks featured in Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (City Hall Loop), so much of the information is repeated so you don’t have to go back and forth between tours/posts.  There’s a condensed free PDF guide at the bottom of this post for easy printing or smart phone viewing.  And if you need a super quick geology precursor, you can find that here: Geology Basics: For the Casual Observer or Amateur Enthusiast.  Enjoy, fellow rock lovers!

WELLS FARGO – 1000 LOUISIANA

Flooring

Marble (white with grey veins, metamorphic)

Walls/Patio

Granite (red/pink, felsic igneous)

Poikilitic texture in the tunnel interior, granite with pegmatite veins on the patio pavement

Water Wall

Anorthosite (grey/tan, intermediate igneous)

Contains dark minerals and some labradorite

Accent Column

Larvikite (intermediate igneous)

Specific variety of Monzonite, for thumbnail-sized feldspar

From Larvik Batholith in the Oslo Rift in Norway (Permian, 292-298 my) or Killala Lake Alkalic Rock Complex near Thunder Bay in Ontario, Canada

Could be confused with Ubatuba (I did)

Fun Fact

The Wells Fargo Plaza is currently the 20th-tallest building in the United States, the second tallest building in Texas and Houston, after Houston’s JPMorgan Chase Tower, and the tallest all-glass building in the Western Hemisphere

Patio

One of the few buildings downtown connected to a patio via tunnel.  Marble flooring inside, great views of granite accent stone at street level from patio.

Water Wall/Patio Flooring

Water was off on the day we explored the patio.  Veined granite is cut in deceptively large blocks, with smaller blocks carved only on the surface in place.  Dark mineral veins dominant.  Granite could be same or similar to the veined granite on the Houston Public Library (Building 2 in Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (City Hall Loop)).

Pegmatite veins: holocrystalline (roughly), intrusive igneous rock composed of interlocking phaneritic crystals (usually larger than 1”)

Observed: potassium feldspar rich veins and dark mineral veins, contains both pyroxene and hornblende

Anorthosite: an intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), visible to the naked eye (large in this case) with a minimal mafic (pyroxene, ilmenite, magnetite, and olivine) component (0–10%)

ONE SHELL PLAZA – 910 LOUISIANA

Flooring/Walls

Tufa (Travertine, continental sedimentary)

Travertino Romano (trade) from Tivoli near Rome in Italy

Also known as Romano Classico or Travertine Classico and Travertino Romano Antico (darker varieties)

Walls and flooring all travertine

Accent Tiles

Marble (white with grey veins, metamorphic)

Tufa/Travertine: formed by algae/calcium carbonate in hot springs, phytoherms (freshwater reefs) and thrombolite-stromatolites; not to be confused with tuff/tufo (igneous)

Observed: stromatolite patterns/precipitation growth dominant feature, some vugs partially to fully filled with more transparent cement

Note: the tunnel between One Shell and Two Shell (next) was built diagonally to the streets above and connects to a short tunnel to the Lanier Public Works Building (Building 5 featured in Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (City Hall Loop)).  Travertine remains through this section.

TWO SHELL PLAZA – 811 LOUISIANA

Flooring/Walls

Tufa (Travertine, continental sedimentary)

Identical to One Shell (see One Shell for details)

Accent Flooring (below lobby)

New (<5yrs)

Marble (dark metamorphic, likely low-grade metamorphism)

“Dirty” marble with fractures, flow features, and calcite veins

Dirty marble: contains impurities such as clay minerals, iron oxides, or bituminous material resulting in a bluish, gray, pink, yellow, or black color

ESPERSON BUILDINGS – 808 TRAVIS

Baseboards/Wall Accents

Marble (salmon and green-brown, metamorphic)

Multicolored/dirty marble on wall accents and brecciated marble on baseboards

Brecciated marble: broken fragments rolled and rounded by the flow of marble under pressure

919 MILAM

Escalator Walls

Onyx (tan, sedimentary)

Renovated/added in 2006, the escalator entrance at lobby level is now back-lit onyx, a banded variety of the oxide mineral chalcedony

Fun Fact

The first of three buildings in Downtown Houston to be networked in the first phase of a pedestrian tunnel system

Onyx: layered chalcedony that differs from agate only in the form of the bands: agate has curved bands and onyx has parallel bands

TRAVIS PLACE – 1010 TRAVIS

Flooring (light grey)

Granite (light grey felsic-intermediate intrusive igneous)

Color matched: Coldspring Rockville (trade)

From East-Central Batholith in Rockville, Minnesota (assumed)

PreCambrian (1.78gy)

Coldspring Rockville Granite: granite (quartz 20-60% and plagioclase 10-65%) to granodiorite (quartz 20-60% and plagioclase 65-90%)

Poikilitic texture: large component crystals contain smaller crystals of other minerals within them

Observed: large feldspars with poikilitic texture containing dense, dark minerals in almost every slab

Flooring Accent (dark grey)

Granite (dark grey felsic-intermediate intrusive igneous)

Color matched: Coldspring Lake Superior Green (trade)

From East-Central Batholith near Isabella, Minnesota (assumed)

Late Archean (2.8-2.5gy)

Coldspring Lake Superior Green: could be granite, granophyre, ferro-monzodiorite, or leucogabbro…challenging anyone to stick their nose to the rock and give us a more educated guess

Observed: uniform and equal amounts of salt and pepper

Stairs/Accent

Granite (felsic intrusive igneous)

Color/texture match to Sunset Red Granite from Llano uplift in Texas

Phaneritic/ poikilitic pink granite with large rapakivi feldspars and dark mineral clusters

Poikilitic texture: large component crystals contain smaller crystals of other minerals within them, most easily observed in petrographic thin sections

Rapakivi: large rounded crystals of orthoclase that are surrounded by a rim of oligoclase (a variety of plagioclase)

KINDER MORGAN – 1001 LOUISIANA

Flooring (light grey)

Granite (light grey felsic-intermediate intrusive igneous)

Color matched: Coldspring Rockville (trade)

From East-Central Batholith in Rockville, Minnesota (assumed)

PreCambrian (1.78gy)

Coldspring Rockville Granite: granite (quartz 20-60% and plagioclase 10-65%) to granodiorite (quartz 20-60% and plagioclase 65-90%)

Poikilitic texture: large component crystals contain smaller crystals of other minerals within them

Observed: large feldspars with poikilitic texture containing dense, dark minerals in almost every slab

Flooring Accent (dark grey)

Granite (dark grey felsic-intermediate intrusive igneous)

Color matched: Coldspring Lake Superior Green (trade)

From East-Central Batholith near Isabella, Minnesota (assumed)

Late Archean (2.8-2.5gy)

Coldspring Lake Superior Green: could be granite, granophyre, ferro-monzodiorite, or leucogabbro…challenging anyone to stick their nose to the rock and give us a more educated guess

Observed: uniform and equal amounts of salt and pepper

Stairs

Marble (white with grey veins, metamorphic)

Marble veins: due to various mineral impurities such as clay, silt, sand

…and back to Wells Fargo!  Note: at the entrance of Wells Fargo from Kinder Morgan are four marble tiles that have been replaced with new marble tiles that have parallel veins compared to the original, which is more swirled.

Download Free PDF Tunnel Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Red Loop) here: DowntownGeologyRedPDF

Published Walking Tours

Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (City Hall Loop)

Tunnel Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Red Loop)

Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Hyatt Loop)

Tunnel Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Yellow Tunnel)

Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Jones Loop)

Tunnel Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Teal Tunnel)

CONTRIBUTORS

Sheila Echols-Smesny holds a Bachelor of Science in Geology from Sam Houston State University, an Executive MBA from Texas Woman’s University, and works at an oil & gas company in Houston.  Red Shoes. Red Wine. is Sheila’s travel, lifestyle, & hobby blog.

Christen Peevy holds a Bachelor of Science in Geology from University of Oregon and works at an oil & gas company in Houston.  Christen’s lifestyle blog is Short Sweet & Lovely.

Katy Mainwaring holds a Bachelor of Science in Geology from Texas Tech University and works at an oil & gas company in Houston.  Katy teaches geology with Sheila for Texas Parks and Wildlife Becoming an Outdoors Woman program.

BEFORE YOU GO

Safety

• Look up, not at your phone, when navigating downtown
• Please be mindful of the traffic lights, pedestrian signals, bike lanes, and buses
• Buses make frequent stops and can sometimes hop curbs
• Some curbs, pavements, and streets may be uneven

Etiquette

• Please review the walking guide prior to arriving downtown to maximize time spent on the tour
• Please be mindful of downtown employees and keep slower pedestrian traffic to the right so they can go about their business
• Try to walk in pairs if walking around downtown as a group
• If approached by a homeless person, try to be firm but respectful

REFERENCES

• Houston Geological Society, 1995, Walking Tour of Downtown Houston Building Stones: Research Committee, Philip W. Porter
• Houston Gem and Mineral Society, Houston Geologic Society, 2008, Walking Tour – Houston Building Stones, Neal Immega
• Fossils in the Architecture of Washington, D.C.: http://dcfossils.org/index.php/gallery11/#origins
• United States Geological Survey: https://mrdata.usgs.gov/geology/state/map-us.html
• Wikipedia
• Geology.com

Coming soon…

Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Bayou Loop)

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