Excellent question - I’d have expected that to be referenced, but it isn’t. Nor is it in the article by Oard that @PDPrice relied on.*
Looking elsewhere finds this:
However, it has been noted that 43 of these arches have collapsed during a 45 year period (1970-2015), a rate of about one collapse per year. (2)
which leads to this:
They’re right to suggest that if you want to see Arches National Park’s ‘celebrity rocks’, you’d better hurry, as just since 1970 at least 43 of its arches have collapsed.
which leads to this:
43 arches have collapsed since 1970, yet still the beauty of nature here will leave you in awe. … I have recently read that since 1970 43 arches or land bridges have crashed to the ground in Arches National Park.
which doesn’t reference any source other than an NPS website that hasn’t been completed.
Following a different rabbit trail starting here leads to this which doesn’t mention anything relevant.
This site gives the data as 1977, not 1970, but no reference.
Michael Conrad committed the claim to print in 2017, again with no reference.
The claim is also given here, which leads nowhere, and here which leads to a since-removed comment on Wikipedia that was added in March 2006 by an anonymous user going by “rocky mountain np” who made only that one edit anywhere on Wikipedia, and didn’t reference it.
So basically, all these references (and several others I haven’t included here) to 43 arches collapsing since 1970 have their roots in a single unreferenced removed Wikipedia comment. There is no way to verify it, no way to know who made it, and no reason to believe it. If some-one wanted to inject a falsehood into Wikipedia to see how far it spread, it would look exactly like this. Even AiG, who are known for their credulity,** are skeptical of it. This entire exercise reduces to a moral tale about relying on Wikipedia rather than using Wikipedia as a route to original sources, and if @PDPrice has any integrity at all, he will revise his article and remove his claim that arches are collapsing at a rate of one per year, because it has no foundation whatsoever.
I’ve noted this in a comment on CMI’s page too.
I found another interesting detail. Oard refers to the natural bridges in Australia as arches - which skewers @PDPrice’s attempt to claim they’re bridges, not arches.
*While checking this I found two apparent errors in Oard’s article. Oard says:
In 1991, an arch off Point Campbell, western Victoria, Australia, collapsed.
But it was actually an arch in Port Campbell that apparently collapsed in 1990. These errors could originate in Oard’s source rather than with Oard, but they’re trivially checkable so he has no excuse.
**cf baboon dogs and the living French pterodactyl.
Added: More digging finds many similar references to 43 arches having collapsed since 1977, but all of them are still more recent than the Wikipedia edit (including this one about a 1992 expedition, but written after 2008). Most attribute the claim to “rangers at Arches National Park”, but I’ve found none that cite a source. One refers to this paper, but checking the text finds it lists only four collapses, and not just in Arches National Park, . There’s a list of collapses here, but if merely refers to the Wikipedia page; since it gives 1977 but cites Wikipedia it may be the origin of the changed year.
All routes back from this claim are either dead ends or lead to Wikipedia - and, as one writer admitted:
Since its inception in 2001, Wikipedia has been a controversial website, plagued with problems, the greatest of which is the serious concern of biased and inaccurate content.
There is one obvious omission from the above links. The claim about 43 arches collapsing since 1970 or 1977 is not found in the one place where it would, if true, be expected to be found: the National Park website.