A state is not a point, and the point this page stands on was chosen carefully. Colorado's own geographic centre sits 95 km from Denver, and the plate model puts the two in the same place at four of the five ages on this page — so a page built there would have been Denver's page again. Cañon City is 146 km away and shares none of its rows. Inside its box are 207 fossils: 169 recorded as living on land against 37 in the sea, most of them at one age around 150 million years ago. This site already has a page about a sea that cut North America in two. This box, 160 km from it, is mostly dry.
Five ages in the past of this place, each one a window rather than a day. Each says which witness spoke — and where our evidence cannot answer yet, it says that too.
“Ma” means millions of years ago. The dashed mark means our sources have nothing for that age — which is a finding, not a fault.
Why this page is not standing in the middle of the state
Every location page on this site is a box around one set of coordinates, and choosing those coordinates is a decision somebody has to make honestly. For Colorado the obvious choice was the state’s geographic centre. It was tested and rejected, and the reason is worth showing you.
The centre of Colorado is 95 km from Denver. Run both through the plate model and four of their five ancient positions come out identical once rounded. A page built there would have carried Denver’s timeline back to you with a different name at the top — and varying the numbers to make it look different would have been inventing them.
So this page stands 146 km further out instead, at Cañon City, whose five rows match Denver’s on none. Same state, genuinely different record.
And it is a different record. 169 of these 207 fossils are recorded as living on land, which makes this box mostly dry — 160 kilometres from a page on this site about a sea that cut North America in half. Those two facts sit next to each other and this page does not join them: our sources do not say that this ground was the shore of that sea, or above it, or anything else about the relationship. Two boxes, 160 km apart, with different things in them.
Travel back in time
These five rows were the reason this page moved. At the state’s own centre four of them would have repeated another page on this site exactly; here, none of them does.
250
million years agojump to the evidence250 million years ago, the plate model puts this ground almost on the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 5.1° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
200
million years agojump to the evidence200 million years ago, the plate model puts this ground about 14° north of the equator. Published models agree more closely here, within about 2.6° of latitude, but it is still one model's answer rather than a photograph.
150
million years agojump to the evidence150 million years ago, the plate model puts this ground about 23° north of the equator. Published models disagree by about 4.3° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
100
million years agojump to the evidence100 million years ago, the plate model puts this ground about 36° north of the equator. Published models disagree by about 3.3° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
66
million years agojump to the evidence66 million years ago, the plate model puts this ground about 42° north of the equator. Published models agree more closely here, within about 1.3° of latitude, but it is still one model's answer rather than a photograph.
What was the water doing?
Five ages, oldest first. Each one has two kinds of witness — the rock of the wider region, and the fossils dug up near the town — and they are kept apart on purpose, because they are answers to different questions.
Each age here is a marker on the timeline, not a single day. The evidence that belongs to it comes with an age range of its own that overlaps the marker — so it can tell you what this stretch of time was like, and never what was happening on one exact date.
Our evidence has no witness here
Around 250 million years ago
250 million years ago, the plate model puts this ground almost on the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 5.1° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
An open question
Neither of the evidence sources we use can answer this one: our regional rock record holds no unit for 250 million years ago at this point, and no fossil dug up nearby covers that age either. That is a real gap in the evidence, not a gap in the past — and saying so is more useful than guessing.
Our evidence has no witness here
Around 200 million years ago
200 million years ago, the plate model puts this ground about 14° north of the equator. Published models agree more closely here, within about 2.6° of latitude, but it is still one model's answer rather than a photograph.
An open question
Neither of the evidence sources we use can answer this one: our regional rock record holds no unit for 200 million years ago at this point, and no fossil dug up nearby covers that age either. That is a real gap in the evidence, not a gap in the past — and saying so is more useful than guessing.
The rock of the region says land
Around 150 million years ago
150 million years ago, the plate model puts this ground about 23° north of the equator. Published models disagree by about 4.3° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
The rock of the region
Across the wider region, the rock from 150 million years ago — the Morrison Fm — was laid down on land, not under the sea. That is a statement about roughly 28,000 square kilometres of region, centred about 39 km from the town — not about the ground under one street.
The fossils dug up nearby
89 fossils dug up near Cañon City have an age range covering 150 million years ago: 1 from the sea, 88 from land. The closest of them was found about 6.8 km away — near the town, never under it.
The regional column spanning 150 Ma is non-marine; the fossils dug up near this place whose age range contains 150 Ma are 1 marine, 88 terrestrial and 0 unclassified. These are different claims about different things — a region tens of thousands of km² wide, and individual digs kilometres away — and both are shown. The nearby fossil record is mixed — it holds both sea animals and land animals whose age ranges overlap this age.
The rock of the region says sea
Around 100 million years ago
100 million years ago, the plate model puts this ground about 36° north of the equator. Published models disagree by about 3.3° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
The rock of the region
Across the wider region, the rock from 100 million years ago — the Graneros Shale — was laid down in the sea. That is a statement about roughly 28,000 square kilometres of region, centred about 39 km from the town — not about the ground under one street.
The fossils dug up nearby
18 fossils dug up near Cañon City have an age range covering 100 million years ago: 17 from the sea, 1 from land. The closest of them was found about 0.7 km away — near the town, never under it.
The regional column spanning 100 Ma is marine; the fossils dug up near this place whose age range contains 100 Ma are 17 marine, 1 terrestrial and 0 unclassified. These are different claims about different things — a region tens of thousands of km² wide, and individual digs kilometres away — and both are shown. The nearby fossil record is mixed — it holds both sea animals and land animals whose age ranges overlap this age.
Only the fossils speak
Around 66 million years ago
66 million years ago, the plate model puts this ground about 42° north of the equator. Published models agree more closely here, within about 1.3° of latitude, but it is still one model's answer rather than a photograph.
The rock of the region
No rock layer from 66 million years ago survives in the regional record here, so the rock has nothing to say about this age.
The fossils dug up nearby
11 fossils dug up near Cañon City have an age range covering 66 million years ago: 2 from the sea, 9 from land. The closest of them was found about 2.4 km away — near the town, never under it.
What was dug up nearby?
Dug up around Cañon City and never underneath it, so every row carries its distance. Read the environment column on this one: it records 169 of these as living on land and 37 in the sea, and those two numbers were not gathered in a way that lets them be ranked against each other.
Around 66 million years ago
A Nostoceras larimerense from around this time (its own age range is 72.2–83.6 million years) was dug up about 8.1 km from here, in the Pierre Shale, Fremont County.
A Baculites reesidei from around this time (its own age range is 72.2–83.6 million years) was dug up about 8.1 km from here, in the Pierre Shale, Fremont County.
A Lepisosteidae from 66 million years ago was dug up about 8.4 km from here, in Fremont County.
Around 100 million years ago
A fossil the database can only call “Dinosauria” from 100 million years ago was dug up about 0.7 km from here.
A fossil the database can only call “Ankylosauria” from around this time (its own age range is 106.3–113.2 million years) was dug up about 0.8 km from here, in the Plainview.
A trace fossil called Caririchnium — a name for a mark an animal left, not for the animal itself — from around this time (its own age range is 106.3–113.2 million years) was dug up about 0.8 km from here, in the Plainview.
Around 150 million years ago
A Mesolocustopsis morrisonensis from 150 million years ago was dug up about 6.8 km from here, in the Morrison.
An Allosaurus from 150 million years ago was dug up about 7.5 km from here, in the Morrison, Fremont County.
A Camarasaurus supremus from 150 million years ago was dug up about 8.9 km from here, in the Morrison (Salt Wash), Fremont County.
We show these places to the nearest few kilometres rather than pinning them exactly. The scientists who recorded them know the spot far better than that — the full record is one click away in the Paleobiology Database, and it is free for anyone to read. We round them here because a map made for children is not a map for digging things up, not because anything is being hidden.
What changed?
The plate model places this ground at every age and carries it north through the page. Where a piece of surface was is not a description of what was on it.
The rock at the surface today is younger than all of it. The geological map of this exact point returns Mesozoic sedimentary rocks (Mesozoic), Late Cretaceous sedimentary (Cretaceous), Modern alluvium (Cenozoic).
This is one box in a state 600 km wide, and the box next door — Denver's — holds a completely different kind of evidence. Neither of them is Colorado.
Try it yourself
The land animals here drank fresh water and the sea creatures lived in salt. It is the same water; what changed is which part of the journey it was on.
This page is about choosing where to measure. Two points 95 km apart gave the same answer four times out of five — a good demonstration that a result can be about your method rather than about the world.
If two places 95 km apart give the same answer, and one 146 km away gives a different one, what does that tell you about how big a 'place' really is?
How sure are we?
Column facts describe an area of thousands to tens of thousands of km², centred tens of kilometres from the town coordinate. They are claims about a region, never about the rock beneath the town.
Fossil facts are a bounding-box sample around the town, each with its own distance from it; a fossil is never "here". The absence of fossils is not evidence of the absence of life — only of the absence of a recorded, published dig in this box.
Positions are model outputs, not observations. Independent plate models disagree by hundreds of kilometres at these ages, and that spread is the honest size of the uncertainty.
The land/sea question is answered only by the regional rock and the local fossils, separately, and never by the reconstruction — which says where this ground was and cannot say whether it was wet. There is deliberately no single field holding a one-word answer, because answering in one word would require merging a regional claim with a local one (CLAUDE.md rule 5). The nearby fossils are reported as a census of what has been found — which kinds are present, and how many of each — and never counted into a verdict: occurrence records are not statistically equivalent observations, so a plurality of them cannot establish an environment (science review, 2026-08-30).
Fossils are binned to their nearest slice age by age-range midpoint, with boundaries at the inter-slice midpoints 83, 125, 175 and 225 Ma. Those boundaries are an editorial choice, not a published stratigraphic scheme; a reviewer may prefer stage boundaries. Every occurrence keeps its own age range so the choice can be re-examined.
Sources
Macrostrat — the rock of the regionRead from version 2.3.9 of its data service on 2 September 2026.Peters, S.E. et al. Macrostrat: a platform for geological data integration and deep-time research. https://macrostrat.org, accessed on (date)Palaeogeography: Wright, N., Zahirovic, S., Müller, R. D., and Seton, M. Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics. Biogeosciences 10:1529-1541
The Paleobiology Database — the fossils dug up nearbyPBDB publishes no dataset version string; the data-service path (data1.2) and the datainfo access_time bound this claim.Fossil occurrence data from the Paleobiology Database (https://paleobiodb.org), released under CC0 1.0.Palaeo-coordinate cross-check (Paleobiology Database `pgm=gplates`): Wright et. al., 2013; Towards community-driven paleogeographic reconstructions.Palaeo-coordinate cross-check (Paleobiology Database `pgm=scotese`): Scotese, C.R., 2021. An Atlas of Paleogeographic Maps: The Seas Come In and the Seas Go Out, Annual Reviews of Earth and Planetary Sciences, v. 49, p. 669-718.Palaeo-coordinate cross-check (Paleobiology Database `pgm=seton`): Seton et. al., 2012; Global continental and ocean basin reconstructions since 200 Ma.
The EarthByte plate model — where this ground used to beMULLER2019 version 3.0, run with pyGPlates 1.0.0, licensed CC BY 4.0.GPlates: Müller, R. D., Cannon, J., Qin, X., Watson, R. J., Gurnis, M., Williams, S., Pfaffelmoser, T., Seton, M., Russell, S. H. J., Zahirovic S. (2018). GPlates: Building a virtual Earth through deep time. Geochemistry, Geophysics, Geosystems, 19, 2243-2261. https://doi.org/10.1029/2018GC007584Reconstructions computed with the GPlates Web Service (EarthByte Group, The University of Sydney).Plate model: Müller, R. D., Zahirovic, S., Williams, S. E., Cannon, J., Seton, M., Bower, D. J., Tetley, M. G., Heine, C., Le Breton, E., Liu, S., Russell, S. H. J., Yang, T., Leonard, J., and Gurnis, M. (2019), A global plate model including lithospheric deformation along major rifts and orogens since the Triassic. Tectonics, vol. 38, https://doi.org/10.1029/2018TC005462. Licensed CC BY 4.0.Plate model: Zahirovic, S., Eleish, A., Doss, S., Pall, J., Cannon, J., Pistone, M., Tetley, M. G., Young, A., & Fox, P. (2022). Subduction kinematics and carbonate platform interactions. Geoscience Data Journal, 9(2), p.371-383. Licensed CC BY 4.0.Coastline and static-polygon data by the EarthByte Group, licensed CC BY 3.0 Unported.
This record was assembled on from the datasets above. The ancient positions are reconstructions from a published plate model, not observations.
