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A Creation Ministries International article makes the following claim about the multiple-local-flood explanation for the deposits at the Morrison Formation:

The idea of many local floods might at first seem a possibility.
However, a notable feature of the water-worked sandstone in which the
dinosaur bones are entombed complicates the picture for
uniformitarians—these rocks contain abundant grains of a rock called
‘tuff’. Tuff forms from the solidification of hot ash ejected from
volcanoes. This, and layers of volcanic ash elsewhere in the
formation indicate that an explosive volcanic eruption occurred at
much the same time as all the dinosaur remains were buried by
flooding. No volcano is known in the vicinity of the deposit, and
geologists have placed the nearest source for the tuff to vents in
southern California or Nevada. Ash clouds depositing over such
considerable distances point to an extremely catastrophic volcanic
event.

The coincidence of floods and eruptions happening together on multiple
occasions, over vast spans of time, stretches the credibility of the
uniformitarian ‘just so’ story.

Has tuff been found amongst the deposits at the Dinosaur National Monument? Is this incongruous with the scientific consensus that the fossils were produced at various times hundreds of millions of years ago, rather than all at once in a worldwide flood event?

Has tuff found amongst the deposits at the Dinosaur National Monument?

Yes. The most famous section of the rocks in Morrison Formation in Dinosaur National Monument, the Brushy Basin Member, is chock full of volcanic ash beds that have long since been converted to rock (1, 2, 3). It's also chock full of dinosaur fossils, which is what makes it so famous.

Is this incompatible with the theory that fossils were produced hundreds of millions of years ago?

Not just no, but emphatically no. In fact, exactly the opposite applies. Those many volcanic ash beds are the key to precisely dating the various parts of the Bushy Basin Member (1, 3, 4) to 148 million years old at the top of the member to 150 million years old at the bottom (4). At that time, what would become the Great Basin (i.e., just west of where Dinosaur National Monument is now) was colliding with the subducting Farallon Plate, forming a chain of volcanoes to the west (3) that occasionally dropped ash (and sometimes a lot of ash) on the area where Dinosaur National Monument is now.

The referenced Creation Ministries article makes a straw man parody of uniformitarianism to which no geologist or biologist ascribes. There have been times in the Earth's past where catastrophes have happened (e.g., the Chicxulub impact, the Deccan traps, the Siberian traps). Perfect uniformitarianism is a nonsense concept. The basic concept of uniformitarianism is not a nonsense concept. It remains a cornerstone of geology, biology, astronomy, and cosmology.

The globe looked just a bit different at the time the Brushy Basin Member formed than it does today.

References:

1. Christiansen, Eric H., Bart J. Kowallis, Michael J. Dorais, Garret
   L. Hart, Chloe N. Mills, Megan Pickard, and Eric Parks. "The record
   of volcanism in the Brushy Basin Member of the Morrison Formation:
   Implications for the Late Jurassic of western North America." Geol
   Soc Am Spec Pap 513 (2015): 399-439.


2. Bell, Thomas E. "Deposition and diagenesis of the Brushy Basin
   Member and upper part of the Westwater Canyon Member of the Morrison
   Formation, San Juan Basin, New Mexico." in SG 22: A Basin Analysis
   Case Study: Morrison Formation, Grants Uranium Region, New Mexico
   (1986): 77-91.


3. DeCelles, Peter G. "Late Jurassic to Eocene evolution of the
   Cordilleran thrust belt and foreland basin system, western USA."
   American Journal of Science 304, no. 2 (2004): 105-168.


4. Kowallis, Bart J., Eric H. Christiansen, Alan L. Deino, Fred
   Peterson, Christine E. Turner, Michael J. Kunk, and John D.
   Obradovich. "The age of the Morrison Formation." Modern Geology
   22, no. 1-4 (1998): 235-260.