The Great Inland Seaway

The Great Inland Seaway (HMJE8)

Location: Atlanta, MT 30345 Stillwater County
Buy Montana State flags at!
Country: United States of America
Buy United States of America flags at!

N 45° 36.025', W 109° 3.958'

  • 0 check ins
  • 0 favorites
For over sixty million years during the Cretaceous Period, much of eastern Montana was underwater, covered by an vast inland sea. As the Rocky Mountains formed to the west, it created a broad, flat coastal plain that was home to many different species of dinosaurs. Indeed, the long life of the sea saw the rise and extinction of many dinosaur species until it finally receded from Montana about 65 million years ago at the end of the Cretaceous Period. The sediments deposited underwater or along the sea's coast formed the spectacular sandstone rimrocks in the Yellowstone River valley between Columbus and Billings.
The sea was shallow and warm, probably no more than a few hundred feet deep. But it was home to a wide variety of aquatic life. Oysters lived in dense banks along the shore, while tentacled ammonites fed on monster clams that lived in the shallow water offshore; sharks also cruised the shallows preying on whatever animals appeared tasty to them. For several million years, two predators, synonymous with prehistoric sea creatures, were at the top of the food chain in the sea: the long-necked Plesiosaurs and the snakelike Mosasaurs. Neither animals were dinosaurs, but were air-breathing reptiles who had adapted to living in the oceans. Both were carnivores that ate just about anything they could seize and swallow. Fossils of Plesiosaurs and Mosasaurs have been found throughout eastern Montana.
For centuries, the sandstone rimrocks along the Yellowstone River guided travelers between the mountains and the buffalo country to the east. In 1912, regional Good Roads enthusiasts and county officials created one of the first interstate highways in the United States, the Yellowstone Trail, an interconnected network of county roads blazed by distinctive chrome yellow signs with black arrows. The 4,000-mile highway connected Plymouth Rock, Massachusetts and Seattle, Washington with a branch to Yellowstone National Park. Later re-designated U.S. Highway 10, Interstate 90 bypassed it in 1971.
HM NumberHMJE8
Placed ByMontana Department of Transportation (MDT)
Marker ConditionNo reports yet
Date Added Tuesday, September 16th, 2014 at 7:48am PDT -07:00
Sorry, but we don't have a picture of this historical marker yet. If you have a picture, please share it with us. It's simple to do. 1) Become a member. 2) Adopt this historical marker listing. 3) Upload the picture.
Locationbig map
UTM (WGS84 Datum)12T E 650830 N 5051471
Decimal Degrees45.60041667, -109.06596667
Degrees and Decimal MinutesN 45° 36.025', W 109° 3.958'
Degrees, Minutes and Seconds45° 36' 1.50" N, 109° 3' 57.48" W
Driving DirectionsGoogle Maps
Area Code(s)404, 678, 770
Closest Postal AddressAt or near 106-198 Ronan Ranch Rd, Atlanta MT 30345, US
Alternative Maps Google Maps, MapQuest, Bing Maps, Yahoo Maps, MSR Maps, OpenCycleMap, MyTopo Maps, OpenStreetMap

Is this marker missing? Are the coordinates wrong? Do you have additional information that you would like to share with us? If so, check in.

Check Ins  check in   |    all

Have you seen this marker? If so, check in and tell us about it.

Comments 0 comments

Maintenance Issues
  1. Is this marker part of a series?
  2. What historical period does the marker represent?
  3. What historical place does the marker represent?
  4. What type of marker is it?
  5. What class is the marker?
  6. What style is the marker?
  7. Does the marker have a number?
  8. What year was the marker erected?
  9. This marker needs at least one picture.
  10. Can this marker be seen from the road?
  11. Is the marker in the median?