In the short term they might survive, on the long term they are screwed
There are a lot of things that can go wrong if a 20th century Wyoming-Montana town got transported to the Campanian period. Also for references check out my answer on (this question), which covers a lot of the same things.
Some of these problems include:
A lack of edible vegetation among the native flora
You got really, really lucky by proposing the Campanian as your time period of choice. The Campanian is the point in time that the conifer-dominated floras of the Mesozoic were replaced by the angiosperm-dominated faunas that characterized the Cenozoic or later. Campanian-Maastrictian forests would have looked essentially modern with an odd abundance of gingkos and dawn redwoods.
However, the broader problem is that most of the edible plants we know and love had not evolved yet by the Campanian. Most edible fruit and nut-producing plants hadn't evolved yet, because these plants evolved their edible seed coverings due to coevolution with primates and other fruit-eating Cenozoic animals. Maples (maple syrup) and oaks (acorns) also hadn't evolved by the Campanian.
Your sources for native vegetation are going to be few.
- Sago palm (very toxic if not cooked properly)
- Pine nuts
- Fern fiddleheads
The good news is that the native wildlife should be fine to eat as long as it's sufficiently cooked. Disease transmission from eating dinosaurs should be low, though not completely impossible. Meat is meat and hasn't changed its structure in hundreds of millions of years. Dinosaur meat should be as safe to eat as alligator or chicken. Large animals generally don't have toxic meat because it costs a lot, metabolically speaking. The biggest thing to worry about would be if the local animals have accumulated arsenic or heavy metals in their tissue due to the plants they ate. But this is unlikely.
Huge risks for crop failure
So, the thing about Wyoming and Montana is there isn't a lot of crop farming there. It's some of the driest territory in the lower 48 outside of outright deserts like Nevada and most farming there today is restricted to areas where it's easy to get water, especially around large rivers like the Missouri and North Platte.
So very few crops are going to be taken with this town into the Cretaceous, which raises the risk of a single wheat blight or corn smut completely wiping out the town's food supply. In the 20th century if you have a mass crop failure you can always replant the wheat and corn fields with seeds from elsewhere. In the Cretaceous you can't.
Wait, there's more. The Cretaceous lacks any native pollinators for major crops like butterflies and bees. Good news is that major American staple crops like wheat and corn can self-pollinate or pollinate via the wind and thus don't need bees. However any crops that do need pollinators like apples or most other domesticated plants would be highly dependent on whatever few bee hives or wandering butterflies were grabbed by whatever cosmic power dragged the town back into the Cretaceous. The survival of the pollinators, like the crops, would be heavily dependent on whether they are lucky enough to not get snapped up by some Cretaceous insectivore.
Wyoming and Montana's biggest agrarian output, bar none, is cattle, with sheep also being important in some areas. This means cattle are going to be the town's main source of food unless they can start reliably hunting dinosaurs, especially given they can't supplement their diet using local flora and wheat and corn supplies will be limited.
As with domestic crops, cattle will be highly vulnerable to being wiped out by disease given how few of them there are. One cow with foot-and-mouth disease might end up wiping out your entire herd.
The bigger problem will be native predators. Big predators like theropods will be leery of novel prey like cattle but eventually they will figure out they are viable food sources. Grizzlies, coyotes, and wolves in modern Wyoming and Montana rapidly figured out that cattle were easy prey, despite their ancestors having never seen domestic cattle before. This will be amplified by the fact that cattle ranching practices in Wyoming and Montana often involves just leaving cattle where they die rather than disposing of the body. This will result in native predators having an easier time associating cattle with food (This is one reason why modern ranchers in Wyoming sometimes get wolf problems). The native predators will also lack any intrinsic fear of humans.
Once the theropods do figure out that cattle are easy prey, it's open season on the cattle. Cattle are almost the ideal prey size for large predators like tyrannosaurs, being about the size of a juvenile hadrosaur. Additionally, the cattle breeds used in the 1920s-1930s in Wyoming and Montana tended to be the more docile breeds used today rather than the more aggressive semi-feral breeds such as the Texas longhorn. Longhorn will fight back against predators, more modern beef cattle like Angus are so docile that (in Wyoming mind you!), they've been known to see their calves slaughtered right in front of them by coyotes and do nothing about it. They won't meaningfully fight back against a tyrannosaur.
Another problem is that cattle waste might not break down. There were likely dung beetles and other decomposers would be around, but they would be adapted to breaking down dinosaur dung, not mammal dung. So what would end up happening is you would get massive pile-ups of cattle dung that would never go away. This is what happened in Australia, where you had cattle dung just plain not decomposing because the native dung beetles preferred marsupial and bird dung. The only way this wouldn't happen would be if you brought enough modern dung beetles with you, but even then the small founder population might end up shredded by small mammals and reptiles and go extinct.
It's open for debate whether your cows would even be able to survive long-term. Wyoming thrives because it has huge areas of grassland with little water, and there isn't much else you can do with them than use cows to turn that grass into edible calories. It's not clear if they could do the same in a world where most of that grass has been replaced by ferns, horsetails, and relatives of cannabis. Some edible plants like buttercups and nettles might be around, but its unclear how much. Some native plants might have anti-dinosaur toxins and be lethally poisonous to cattle. The large quantities of herbage necessary to support cattle herds might not be present.
Enjoy your scurvy
This brings up a bigger problem. Your people will eventually start suffering from massive vitamin deficiencies. A diet composed solely of dinosaur meat, beef, and edible grains with no fruit or leafy vegetables anywhere in sight would soon be suffering from scurvy.
Best options? Hopefully some of the rare orchards that exist in Wyoming or Montana might have survived. Alternatively you might be able to figure out some part of native wildlife that has vitamin C and start eating that for all it's worth, like how the Inuit survived on a solely meat-based diet by eating animal liver, brain, and seaweed.
Gradual loss of advanced technology
Towns in the American West in the early 20th century weren't full self-sufficient. They were heavily dependent on the railroad sending raw material out of the town in exchange for machinery and processed goods being brought in. This includes things like gunpowder/firearms, gasoline, farming equipment, etc. Neither Wyoming nor Montana have never had much of a manufacturing industry.
What would end up happening in the long term is that your 20th century technology would break down due to long-term use and inability to replace them. More notably, eventually you would just plain run out of gunpowder to use for firearms.
Insufficiently powerful firearms
One problem you might have is that people might not have powerful enough firearms to meaningfully ward off dinosaurs. By the time of the Great Depression the largest mammals like bison and grizzlies were restricted to the Yellowstone Basin, and animals like wolves were outright extinct in Wyoming until they were reintroduced. Most firearms people had are going to be hunting rifles with the caliber tailored for hunting bighorn, elk, mule/white-tailed deer, and pronghorn. Maybe something like a Winchester. Is a Winchester going to stand up against a Daspletosaurus or an angry ceratopsian?
Best option for long-term survival? Revert to a seminomadic hunter-gatherer lifestyle with some herding and spend your time eating baby dinosaurs and dinosaur eggs, which should be everywhere because dinosaurs are explosive breeders. Supplement with what little cattle survive as necessary. Based on what technology is available to a 20th century Wyoming/Montana town (e.g., ferriers), you might be able to retain iron working and use iron spearheads and arrows.