Native range ends way down in extreme southern Oregon, just north of
California - although exclusion by faster growing hemlock seedlings may
be a factor - young seedlings are slow-growing. And also prone to frost (and drought) - even the largest local examples are burned by colder winters here.

So Ogden, no way.

Yeah, probably not long term but with the mild winters we've been having I'm willing to bet this one will be alive for quite a few years. Some sources say they're killed at 7F but I know of cases where they've pulled through 0 or slightly below (with some damage of course).

Able to grow from stumps.

I think at the latitude of the Rogue Valley 2000 ft. is where the valley climate gives way to the mountain climate, so farther south somewhere in California the coastal/lowland/valley climate might go above 2000 ft. And the way the tree generally sticks to the banana belt I'd think that it being present natively in a location would by definition indicate that location was outside of the cold winter area - that in effect there was no cold part of the specie's native range. Especially when hardiness multiple zones lower than the core native area is being looked for.

The decimating winters here (Seattle area) are those which drop below 10 degrees F., into single digits. The last one of these of which I am aware was in 1990. Also when sharp cold comes early (November 1955, November 1985, November 1990) there is much damage to certain plantings, sometimes a lot of different kinds of certain plantings (1955, 1990) - back when the card files of the Seattle arboretum were publicly accessible I found them to be full of records of pre-1955 plantings that had been lost that winter. And in 1990 - a killing winter I was present for - I saw that damage to broad-leaved evergreens other than hardy rhododendrons, holly-leaf osmanthus, heathers and a few other expected stalwarts was general. Coastal California origin tree and shrub species such as coast redwood, tan oak and California myrtle (Umbellularia) were all browned, despite them being represented here by large examples dating back decades (including coast redwoods over 100 ft. tall). So, same as with your redwood burning at 5 degrees F. when it gets down into that range here plants in this set start to check out. Anywhere where it repeatedly gets significantly colder than that it would seem that coast redwoods were not possible - at least as fully functioning landmark trees.

Unless there really are certain individuals that are much hardier than usual, perhaps under the right year round conditions - including Californian summers.

Yes, yes we've discussed this ad nauseam, the irony or twist or whatever you want to call it is that this plant certainly does not need California summers. It doesn't need them to survive and it doesn't need them to have an extra shot at surviving cold winter. Believe me I'll be the first to admit when something from a dry summer climate is ungrowable. Before the 2nd great freeze we had the wettest June ever here, it killed some of my newly planted stuff and caused a huge 40' Morus to defoliate but apparently survive. None of the redwoods are in a particularly well draining spot (though neither are they in swamps) and they all made in through the following winter that was horrendously cold. I remind you that during some ice ages the glaciers came about as far south as the WA/OR border. Certainly S. s. has a "genetic memory" to survive much colder conditions than its current zn 9-10 haunts. 2500' ft. in the coast ranges wouldn't be very cold but the worst frost hollows at that elevation could certainly be into zn 8 territory and then the plants surviving zn 7 on the east coast doesn't seem so far fetched. In the Great Freeze of 1990, a low altitude location in Marin County reached an astonishing 4F! The Bancroft Garden in Walnut Creek was something like 12F. And that's just what we know in recent human history.

It's a known fact that 'Chapel Hill' survived a verified -9F in, what was it, 85? It was already a large plant then, nobody was covering it with Tyvek and warming it with orchard smudge pots LOL. As I said the Barnes tree surely saw temps around 0F more often. I'm not saying mine will survive another winter like 1899 but I'm saying they will probably survive well enough during my lifetime. Knock on wood (this winter is now over with respect to potentially catastrophic freezes) but it's fascinating that as bad as the past two winters were, as well as this brief spell of this one, it hasn't gone below 0F here when it certainly did in 85 & 94 and several other cold winters back to the infamous 1899, when the Atlantic froze as far south as Virginia Beach. Has something fundamentally changed?* I don't know but by the time I find out it hasn't I predict my redwoods will be big enough to survive almost any winter this area throws at them.

* to clarify, I mostly think I just got lucky, but I can't rule out that something could mean that for a few decades we have, I don't know, a pattern of longer winters that don't get quite as cold, versus shorter winters with more serious freezes. Of course I much prefer the former. I also think my research in where to place this garden paid off: I had a vague sense 11 years ago that I should avoid totally flat terrain and that has been a good choice as is evidenced by vast swaths of the interior Delmarva going below 0F in one of the prior winters because the cold air had nowhere to drain.

Anyhow back to the original poster, sure he might coddle one along in a milder part of Utah for a while. An equally significant or even more significant issue there would probably be their thirst rather than their cold tenderness. They can grow in Sacramento but they need supplemental water - to the roots mind you. Even in summer, because they aren't getting the fog belt moisture. Here even in the summers that were dry by my standards, a moisture-retentive humusy soil and consistent atmospheric moisture meant that I hardly ever had to water them. With very warm water nearby, dewpoints hardly ever drop here in summer, and high dewpoints mean they transpire less water, therefore needing less ground water than they would need in the arid interior west.

And in ~1972 a cold front blew down to northern California and wiped out a bunch of big-leaf rhododendrons that had been growing there for years - as elsewhere, they do have occasional plunges there that nail exotics that have been around for awhile. Otherwise, there's a big difference between one or two cold nights in California or elsewhere in the south followed by an immediate return to summer or at least spring like warmth - and the deeply penetrating cold that freezes root zones in the genuinely cold winters of climates like USDA 7 (average lows between 0 and 10 degrees F.) and below. A palm coming through 17F once or twice in Sacramento does not demonstrate that it will be hardy anywhere it gets that cold, no matter how many times - or for how long - it gets that cold and what other factors are present. Any coast redwood that is not a clone of a proven exceptional specimen that has come through decades of cold winters outside of the normal area of adaptation - without being made to look derelict in the process - must be assumed to be unable to cope adequately with cold winters until many, many years of testing demonstrate otherwise.

Here and there among the many landmark Sierra redwoods in my area dead tops appear from time to time. Presumably this is failure of them to mature adequately during our cool summers. Development of full levels of hardiness can also be affected by soil conditions and what kinds of bacteria or fungi are present on plant bodies. Pseudomonas (lilac blight, bacterial blight of maples etc.) for instance, while not actually a pathogen causes damage by attracting ice during autumn in places where the damp and cool conditions it enjoys are present at that time.

Redwoods used to grow all over the world and now live as wild plants in the comparatively small areas they do now because things got too lively for them elsewhere. Like perhaps most cultivated trees planted thousands of miles from their home ranges coast redwoods growing on the other side of the country are visitors, staying until the accommodation is no longer comfortable - whenever that is, be it 10 months, 10 years or 100.

"Any coast redwood that is not a clone of a proven exceptional specimen
that has come through decades of cold winters outside of the normal area
of adaptation - without being made to look derelict in the process -
must be assumed to be unable to cope adequately with cold winters until
many, many years of testing demonstrate otherwise."

Yes, that's exactly why I pointed out the Chapel Hill tree has survived since the 1930s in NC, including winters down to -9F. OTOH I've grown 'Soquel' - collected near the southern end of the range as I'm sure you know - and in the past two very cold but not extremely cold winters, the degree of damage was about the same. Trust me, the ground was frozen solid, for weeks in the case of 2013-2014. Something that clearly doesn't happen in their native range. I think the facts speak for themselves that these trees are (as are most temperate and many subtropical ones) hardier than they "need" to be for their native habitat.

I've also not concealed that a primary source book noted that 5 or 6 tried in the Philly area's posh public gardens, starting in the early 1900s were all dead by the 1940s. However there could be a number of reasons for that beyond, "when correctly cultivated, they died in cold winters". Maybe the hot summers of the 1930s were the problem, although mine did ok in 2010-2012 which was considered the hottest string of summers since that era. Maybe my benign neglect suited them better to some erstwhile newfangled plant nutrients someone applied back then. I don't know. I'm presenting all the information I have. For me in my garden at the southern tip of the Philadelphia CMSA, they are not particularly difficult to grow.

"Coastal California origin tree and shrub species such as coast redwood, tan oak and California myrtle (Umbellularia)
were all browned, despite them being represented here by large examples
dating back decades (including coast redwoods over 100 ft. tall)."

I would just point out that as a hexaploid (!) conifer we'd somehow expect S. s. to be tougher than the other CA species you list. I see a lot of winter damaged plants around my garden as you might expect, and I can tell you, S. s. wasted no time in starting the recovery process. Almost everything else that was injured for me took longer to recover. I am sure tan oak and CA myrtle would not have survived the two prior winters. At the very best they would have slowly struggled back from the roots. In fact they would really be challenged with normal winters here, too. Which are zn 7 and not zn 8 as yours are. S. s. is clearly a rather special plant in terms of its toughness versus the area it comes from.

Actually, slight correction, the Faris book noted that ONE S.s. was still alive in the 1940s. So 1 of 5 survived the 1930s...hot summers, cold winter (1934).* BUT, when I then tried to track down that tree, it was evidently no longer alive. I think it was at the Tyler Arboretum but when I contacted them they said they did not have a S. s. A logical question would be is it somehow connected to the Barnes tree...maybe grown from a cutting of the 1940s survivor. The Barnes curator told me he knows nothing about it beyond the year it was planted. I've been given the name of a retired horticultural professor in the Philly area who supposedly might be able to get this all sorted out, but I never pestered him because from my POV the issue is academic. I don't "need" the Barnes clone because Atlanta, Soquel and Swarthmore Hardy/Chapel Hill are proving hardy enough.

* it's also worth observing that public gardens tend to remove things that are merely damaged, so that John and Jane Q. Public don't get discouraged by seeing a dead looking plant. Even if it would have recovered it 2 months time. You will never see anything that looks winter damaged at Longwood, believe me. I think that's part of the reason they have so few Camellias planted outdoors in the public areas, including their own 'Aida', which was practically undamaged for me and is imputed to be the hardiest C. X williamsii.

Lastly I hadn't even mentioned two well over 50' trees in the DC area, randomly brought back from roadside vendors in redwood country. Again, obviously not specially selected for hardiness yet both surviving at least '94 and '85 when temps went well below 0F. One is ironically enough near the garden of the man who is the 'grand maitre' of DC rare plant collecting, who was trying uncommon stuff back in the 70s when most of us were babies. Caesalpinia he collected himself in west Texas? Dead after winter 1978. Anyhow, he had no connection to it other than luckily spotting it a couple years before he moved out of that neighborhood of Silver Spring!

Those are Giant Sequioa in DC. They have cold hardiness to Zone 5. Coastal Redwood is another species. Hexaploid as stated above and are only hardy to zone 7. The lumber of the coastal redwoods is highly sought after for their resistance to rotting and rigidity, fast growing, clear runs, tensile strenght and light weight. While Giant Sequioa grows high in the Sierra Nevada range; that lumber dose not have high tensile strength and splinters, but is still rot resistant therefore; is not useful in lumber except for shingle shake. Noe maybe if somebody hybridized a Coast Redwood with Bald Cypress. Now that'd be something to try.