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

After: Downtown Above & Below Map – Office & Tunnels (https://www.downtownhouston.org/maps/?1)

I’ve worked in the oil & gas industry in Downtown Houston for over 15 years.  Like many others, every day I walk past buildings covered in 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 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 before triple digit temperatures prevent us from leaving the comfort of our air-conditioned offices.

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 one of several self-guided walking tours: Hyatt Loop.  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!

WEDGE INTERNATIONAL – 1415 LOUISIANA

Building Base

Granite (dark pink, felsic-intermediate intrusive igneous)

Probably from South Dakota (very similar to Houston Public Library)

Pegmatite veins dominant

Only the base is granite, the building itself is faux

New/Accent

Granite (dark pink, felsic intrusive igneous)

Color matched: Coldspring Carnelian (trade) from Milbank, South Dakota

PreCambrian (~2 gy)

Steps

Slate (light grey, low grade metamorphic)

Maybe faux/porcelain, if so it’s well done

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, uniformly parallel veins throughout

New/Accent

Some building base granite slabs have recently been replaced with more uniform medium grained granite in a slightly cooler color and with no veins (very easy to spot the difference) and contains quartz, potassium feldspar, plagioclase feldspar, and biotite

Steps

Recent (<5yrs) addition/upgrade to the building

TOTAL PLAZA – 1201 LOUISIANA

Building

Granite (grey felsic-intermediate intrusive igneous)

Color matched: Coldspring Iridian (trade) from Minnesota

PreCambrian (1.8-1.75 gy)

Fun Fact

The Petroleum Club of Houston occupies the 35th floor of the Total Plaza

Observed: uniform medium grained granite containing quartz, plagioclase feldspar, hornblende, pyroxene

1111 LOUISIANA

Building/Pavement

Diabase/ Gabbro (dark grey-black mafic intrusive igneous)

Fun Fact

In 1995, the building owners added a circle-shaped canopy that is five stories tall, which was designed by Richard Keating who was also the designer of the nearby Wells Fargo Tower

Observed: small grained but visible to naked eye, alternating polished and unpolished on building and pavement

ENTERPRISE PLAZA – 1100 LOUISIANA

Building/Pavement

Granite (pink, felsic intrusive igneous)

Spanish Rose or Rosa Porrino granite from Spain

Carboniferous (359-299my)

Pavement/Accent

Diabase/ Gabbro (dark grey-black mafic intrusive igneous)

Fun Fact

Enterprise Plaza has rose-colored windows to accompany its Spanish Pink granite exterior

Building

Medium to course grained granite with larger porphyritic/poikilitic crystals varying from thumb size to head size

Porphyritic: large microcline phenocrysts

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

Pavement/Accent

Observed: small grained but visible to naked eye, alternating polished and unpolished on fountain and pavement in arc patterns

HERITAGE PLAZA – 1111 BAGBY

Building Accent

Porphyritic Granodiorite (dark salmon intermediate intrusive igneous)

Pavement

Porphyritic Granodiorite (medium salmon intermediate intrusive igneous)

Fun Fact

The granite feature on the top of Heritage Plaza was designed to imitate a Mayan temple and was inspired by the architect’s visit to the Mexican Yucatan Peninsula

Heritage Plaza completed construction in early 1987 and was the last major office building completed in downtown Houston in the midst of the collapse of the Texas markets in the 1980’s

Building Accent

Course grained granite with larger porphyritic/poikilitic crystals

Porphyritic: large microcline phenocrysts

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

Pavement

Course grained granite with larger porphyritic/poikilitic crystals, lighter in color than on building accent but we concur that they are likely from the same or neighboring quarry

Porphyritic: large microcline phenocrysts

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

DOUBLETREE HOTEL – 400 DALLAS

Sign

Marble (dark green metamorphic, medium-grade metamorphism)

“Dirty” marble with fractures and calcite veins

Contains serpentine (green)

Valet

Marble (light green metamorphic, medium-grade metamorphism)

“Dirty” marble with fractures and calcite veins

Contains serpentine (green)

Sign

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

Observed: less broken fragments and more calcite veins than in valet area

Valet

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

Observed: more broken fragments and less calcite veins than on sign

HYATT REGENCY – 1200 LOUISIANA

Valet

Granite (brown felsic intrusive igneous)

Best guess Baltic Brown (trade) from Southern Finland (likely)

Large palm-size rounded and zoned wiborgite rapakivi poikilitic feldspar crystals

Wiborgite: orthoclase crystals that have plagioclase rims (wiborgite or viborgite type, named after the city of Vyborg)

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

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

BOB AND VIVIAN SMITH FOUNTAIN

Fountain

Rhyolite (pink felsic extrusive igneous)

Sign

Granite (pink felsic intrusive igneous)

Color matched: Sunset Red Granite from Texas (trade)

From Granite Mountain near Marble Falls in Texas (assumed)

PreCambrian (>1.37-1.23gy)

Could be same stone as Texas State Capitol Building in Austin

Fountain

Observed: aphanitic texture with few to no visible/distinguishable grains (any visible grains have been weathered out)

Sign

Town Mountain Granite: Coarse-grained, pink, quartz-plagioclase-microcline rock, in part porphyritic with large microcline phenocrysts. Makes up Enchanted Rock granite mass, Gillespie and Llano Counties.

Observed: contains rapakivi and poikilitic feldspars

CHEVRON – 1400 SMITH

Building Base/Pavement/Blocks

Granite/Granodiorite (grey intermediate intrusive igneous)

Color match best guess Coldspring Sierra White from Raymond, California (maybe McGilvray/Knowles?)

Early Cretaceous (111 my)

Landscaping Rocks

Sandstone (transitional sedimentary)

Moss Rock (trade), origin unknown

Fun Fact

Formerly Enron building

Building Base/Pavement

Polished base/blocks and unpolished pavement is granite (quartz 20-60% and plagioclase 10-65%) to granodiorite (quartz 20-60% and plagioclase 65-90%) with uniform medium grained crystals, weathering present

Blocks

Same or similar to building but appears newer with little to no weathering, polished

Landscaping Rocks

Moss Rock: iron rich, well sorted sandstone common as inexpensive landscaping material with weathered surface darker and richer red than fresh unweathered interior

CHEVRON FCU – 1600 SMITH

Building/Pavement

Granite/Granodiorite (grey intermediate intrusive igneous)

Color match best guess Coldspring Sierra White from Raymond, California (maybe McGilvray/Knowles?)

Early Cretaceous (111 my)

Building

Unpolished granite (quartz 20-60% and plagioclase 10-65%) to granodiorite (quartz 20-60% and plagioclase 65-90%) with uniform medium grained crystals, little to no weathering present

Pavement

Unpolished granite (quartz 20-60% and plagioclase 10-65%) to granodiorite (quartz 20-60% and plagioclase 65-90%) with uniform medium grained crystals, weathering present and concentrated around tile/block edges

KBR TOWER – 601 JEFFERSON

Building

Granite/Granodiorite (grey intermediate intrusive igneous)

Color match best guess Coldspring Sierra White from Raymond, California (maybe McGilvray/Knowles?), contains similar appearance and characteristics as Chevron complex, also unpolished

Early Cretaceous (111 my)

Download Free PDF Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Hyatt Loop) here: DowntownGeologyHyattPDF

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

Coming soon…

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

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