How do geologists figure out sedimentary facies?

Do they have to survey every area? For example in southern Colorado Pierre Shale is about 2500 feet while in Morrison Colorado it's 6200 feet.How do geologists figure out sedimentary facies?
Identification of a sedimentary facies (or any rock facies, for that matter) requires an intimate knowledge of the type locality of that particular facies, what major minerals constitute the lithogenics, and what the depositional/erosional/tectonic activity of the region was like since the formation of the facies.





For example, when I was out west I was able to trace the Navajo sandstone throughout the four corners region, from the Grand Canyon all the way up through Utah. There were points where the Navajo was the thickest facies, while in other regions the Navajo was very thin and nearly unnoticeable. In those thin regions, the deposition of the Navajo might not have been as pronounced (sedimentary facies are formed by deposition of sediment), or the facies could have been exposed at the surface much longer than in other regions and subsequently eroded away. You can determine if this happened by looking for unconformities between the Navajo and the facies above it.





However, there are certain characteristics of the Navajo (Aeolian remnants, highly silicic, slight oxidation) that make it the Navajo formation. Despite the varying thickness of the facies, you can trace these rock characteristics throughout the American Southwest. So yes, if a geologist wishes to determine the full extent of a lithogenic facies, they must attempt to trace that facies as far out as they possibly can, which means a lot of survey work.





What most geologists do nowadays is check the state geological maps of the regions they're interested in and look for rock facies that match the facies of the rock they're studying. Oftentimes facies that are the same facies are given 2 different names in different state geological maps. If this occurs, the type locality of the rock is determined (IE, the best-represented sample of that rock), and the facies name is given based on the state the type locality is in.How do geologists figure out sedimentary facies?
The lithology will be the same throughout the unit. In general, geologists don't set out and map a single unit to its full extents, but as several mapping projects are completed, and various interpretations are put together, correlations are made between similar rock types, and these relationships are tested and confirmed.
Well if you think about the level only then it is perplexing. BUT, if you think of the big picture then it becomes more clear.





There was the deposit of material that in both locations tested the same.


So there fore the cataclysmic events that must have taken place to create those Colorado mountains had to happen after the layers were made.





Had the mountains been formed prior to that the layer would not be an even thickness...





So. A massive earthquake had to create the upheaval of the land and make the mountains.


This would be proven if the layers of sediment are seen on an angle as if they were pushed up from underneath.