*Ancient Landscapes of Western North America: A Geologic History with Paleogeographic Maps, Ronald C. Blakely and Wayne D. Hanney. 2018.

February 2026

About the Book

This book is about the tectonic assembly, and I suspect the geomorphology, of what is now the Western United States. In particular, it will use paleogeographic maps – in which the first author is an expert – to describe the sequence of processes. Besides great maps, the book contains a lot of lovely pictures of geologic landscapes.

This book will have some overlap with the book on Canadian geology we read recently – Four Billion Years and Counting – and also with John McPhee’s Assembling California, which we read a couple of years ago. We being me and CJS.

The Book

C1. Introduction.

• Reviews the aim and scope of the book.
• Covers a few fundamentals like the assembly of the North American Craton, and some of its subsequent development especially outside of the regions that will be the focus of this book.
• The book is focused on the Cordillera, basic the region of North American including the western mountain belt, and areas to its west.

Other interesting bits

• There’s a nice map of the North American Craton on page 4. It shows three Archean cratons collided about 2Ga, and are stitched together by accretionary orogens to form the earliest version of Laurentia. The next billion years saw the accretion of various terranes to the south and east of Laurentia.
• Parts of 2 of the 3 Archean cratons (and a little bit of extra crust) forms the Canadian Shield — I’m not sure what differentiates the Canadian Shield from the stitched together cratons — maybe it is the area of that region that is uncovered?.
• When terranes accrete to a continent the often create compressive pressure that initiate an orogeny.
• Thrust/Reverse faults occur when one block of crust is pushed up over another in response to compressional forces. It is called a thrust fault if the angle is < 45°, and reverse fault if ≥ to 45°.
• Detachment/Normal faults occur when on block of crust moves down relative to the other because of extensional forces, with detachment being at a < 45°, and normal if ≥ to 45°. A detachment fault that flattens with depth is called a listric fault
• Autochthon/Allochthon: The fault block that is thrust up over/covered up by the other fault block.
• The Colorado Plateau has remained fixed on the North American craton except for a slight rotation during the Cenozoic. (Is it considered part of the craton or is it ‘on top’ of it — how do you tell the difference?)
• The Colorado Plateau has remained fixed on the North American carton, excepting a slight rotation during the Cenozoic. Is the CP considered part of the NA craton or is it something that sits ‘on top’ of it?

C2. Principles

This chapter reviews the basic principles one needs to understand the book. These include:

• Terranes. A terrane is a complete block of crust that can be shown to have completely different history, age, and origins than neighboring blocks. Terranes that are from far away are often referred to as exotic or suspect terranes. The concept was developed in the 1970’s. By the 1990’s hundreds of terranes had been described, and now the focus is more on groups of terranes. Terranes are classified in terms of their suspected origins, examples being continental fragments, volcanic arcs, mid-ocean plateaus, and so on.
• Suturing and jumping. When a terrane collides with a continent the subduction zone often ‘jumps’ outward — i.e. the original terrane sutures to the continent and ‘clogs’ the existing trench.

Sediment and sedimentary processes. Sedimentary environments are divided into

• continental environments: rivers, lakes, eolian settings, and alluvial fans — usually quartz rich sandstone, mudstone, and shale
• shoreline environments5: beaches, barrier bars, and tidal flats – usually sandstone, mudstone, and shale
• offshore marine environments: Sandstone, mudstone and limestone; may show signs of bioturbation.
• Deep water marine environments: slope rise; abyssal plane; submarine canyon and fan; trench. Turbidites and slump deposits.
• Carbonate deposits form in marine environments, but most prolifically in the absence of mud and sand
• Volcanic sediments — ash, tephra, flows – can be found in any of the environments if volcanism is taking place.

Igneous rocks and processes. The Cordillera contains some of the most extensive deposits of igneous rocks on the planet because of the subduction of the Farallon plate (the largest tectonic plate known).

• Andesite is commonly found in arc complexes.
• The granite batholiths of the Sierra Nevada used to have andesite above them, but it has eroded away.

Ophiolites are a suite of rocks representing oceanic crust that has been shoved to the surface in a process called obduction.

Metamorphic rocks.

• Blueschist is produced during high pressure metamorphism of oceanic crust during subduction.

Cordilleran Margins

There are active plate boundaries characterized by interaction between oceanic and continental crust. The two types of active boundaries are subduction boundaries (which may or may not involve accretion) and transform boundaries — both are commonly found together.

C3. The Cordillera’s Foundations: Paleoproterozoic and Mesoproterozoic Periods: Ca. 1800-1000 Ma.

“fleeting snapshots in the long cavalcade of time…”

• The mental is in motion, at about the same pace as fingernail growth, because of the heat of radioactive decay near the core-mantle boundary.

C4. The Cordillera’s Long-Lived Passive Margin: Neoproterozoic to Middle Devonian Periods: Ca. 1000 Ma-400 Ma

C5. The Antler Orogeny and the First Suspect Terrane: Middle Devonian to Late Pennsylvanian: Ca. 400-300 Ma

C6. The Amalgamation of Pangaea and the Sonoma Orogeny: Early Permian to Early Triassic – Ca. 300-240 Ma.

C7. The Arrival of Wrangellia and the Nevadan Orogeny: Late Triassic to Late Jurassic: Ca. 240-145 Ma

C8. The Continental Arc, Sevier Orogeny, Western Interior Seaway and Flat-Slab Subduction: Cretaceous Period: Ca. 145-65 Ma.

C9. Flat-Slab Subduction, the Laramide Orogeny, Uplift of the Colorado Plateau and Rocky Mountains: Paleocene and Eocene: Ca. 65-35 Ma

C10. Changing Tectonics, Cooling Climates and the Dawn of Crustal Extension: Late Eocene to Early Miocene (ca. 35-20 Ma) .

C11. The End of Cordilleran Subduction and the Formation of the Basin and Range: Early and Middle Miocene: Ca. 20-10 Ma

C12. Interior Basins, Drainage Integration and Deep Incision: Late Miocene to Pliocene: Ca. 10-2.6 Ma.

C13. The North American Cordillera Today: Pleistocene, Holocene and the Anthropocene: Ca. 2.6 Ma to Present.

Views: 3