That sounds like a pretty good reason for why camels would be required because northern Mexico and the American southwest is pretty desert like so they’d be useful
And yet, OTL, when missions to the Colorado River regions were contemplated in the later 18th century, after the Spanish had been in control of Mexico for over 2 centuries, it did not occur to anyone to send some camels to assist either explorers or the missionaries or the soldiers sent out to support and defend the missionaries.
Still less had this been done at earlier times when explorers were searching for legendary "cities of gold." Sensibly enough, if a region was going to be rich enough to support a Cibola worth conquering, presumably the climate would not be arid! Horses would do anywhere worth conquering, was apparently the prevailing wisdom such as it was.
The Spanish were not very interested in expanding into their claimed territory merely to have someone actually in occupation for Spain; if a given claim was not being actively threatened they left it on paper until it became expedient to actually occupy it--and California for instance they did not occupy, until they came to fear that if they didn't the Russians might pre-empt them. But then they were setting up missions along the coast, which would be good enough to block Russian attempts to recruit supporters. Certainly "California" as we conceive it today has extensive tracts in the southeast where camels would come in handy...but the coastal missions need never worry about having hegemony far inland like that, though I suppose a mission was set up in San Bernadino.
I am not sure what motivated the earlier mission arc sent to the Colorado river; they certainly could have used some camels there yet apparently this never came up as any kind of serious plan.
Now had they done so, I suppose one consequence would have been a gradual expansion of the reach of the missionized arc, drawing more missionaries to go beyond the river itself deep into the Great Basin. But this would be a slow process, and it only got started in the mid-18th century, so even if it proceeds apace to say 1850 it only has a century to work. By then feral camel bands might have established themselves and various Basin peoples adopted them beyond the direct political reach of Spain.
I've wondered before how plausible it might be for either a Spanish Viceroyality of New Spain or independent Mexico to hang on to her territory claims west of the ridge line of the Rockies by means of recruiting and organizing auxiliaries among the Native people, with Plains peoples being settled on the east slope of the Rockies and with development of the lands around the Salt Lake supporting both resettled exilic Plains peoples and Basin peoples. Salt Lake is a "tent peg" if you will to the north, with Santa Fe being the "peg" to the south. With a suitable reinforcement of regular Spanish/Mexican troops shuffled in among the native auxiliaries, perhaps Mexico/New Spain can make it quite costly for the Yankees to penetrate to the Continental Divide and therefore give up on making claims. This might not stop the seizure of California--but OTL, forces involved in this maneuvering did come over land; if a layered defense, with strong Mexico-Spanish forces reinforced by Native allies serving as numerous light cavalry blunt and decimate US troops followed by any breaking through being harassed, delayed, tracked and possibly defeated by concentrations of Hispano-Native forces intercepting them before they reach California, then the rebelling and Yankee forces in California are only reinforced by sea, and I would think if Spain or Mexico could orchestrate this Native-heavy defense of the interior borders, they could dispatch more loyalist force to hold California too--especially if the more astute state this implies has minimized Californio disloyalty. Maybe a determined enough US effort can seize California or parts of it and get at least a portion of CA annexed at the peace table--but if US forces must divert to the north to accomplish objectives such as seizing Santa Fe, and then face determined resistance organized to the west and north not utterly dependent on Santa Fe, the Yankees have to try to take the Salt Lake region too to break the line, and perhaps in an ATL where camels have been introduced 100 years before and Spanish/Mexican soft power among the Basin natives is considerable, even losing both Salt Lake and Santa Fe might not be the end of Hispanic/Native lines of communication and bastions in the interior. A major diversion of US force to New Mexico and Utah, and all along the Rocky Mountain front in between, removes force from the main offensive into Mexico itself, and a more competent New Spain/Mexico may limit their successes there too.
I don't doubt that by 1850, the USA can muster sufficient force to bull through, in a long determined war--provided that in the mean time the Americans don't make enemies of Great Britain coming into co-belligerence or full alliance with whoever controls Mexico. But a stronger Mexico (even one that previously slipped up enough for Texas to be seized) would tend to make the option of diverting general Yankee jingoism against Mexico, and toward Britain--as things were OTL it took some fancy dancing on Polk's part to keep the confrontation with Britain peaceful and diplomatic, nor was the USA deeply and unreservedly determined to attack Mexico. If a war focused solely on Mexico proves costly and inglorious initially, settling terms leaving Mexico in far more possession than OTL seems entirely possible, and claiming California as a discontiguous enclave is less likely.
Now against this, first of all the Spanish and the Mexicans were not exactly welcomed with open arms by Native people. Perhaps by the mid-1840s substantial numbers of them in the Basin interior can be convinced the Hispanic devil they know is greatly preferable to the Anglo devil they know of by terrible rumor, especially if over the course of a century missionary efforts supplemented by Spanish/Mexican troops using camels pursuing a very judicious policy of conversion by persuasion and bribery through favorable trade terms can improve these relations over the OTL prevailing standards; if they can do that in the great northern interior, perhaps Native-Hispanic relations in New Mexico are much better.
OTL the people, even the highly Hispanized elites of Nuevo Mexico, were dismayed and outraged by false rumors that Santa Anna proposed to sell NM to the USA to buy the Yankees off general war with Mexico, and gave no resistance to the invading US troops sent to secure Santa Fe. Later, not much later, they became dismayed at blatantly bigoted treatment and offered some resistance but by then it was a bit late for them. NM's Mexican garrison was a pathetically tiny force too. But if that garrison were more in line with the value of NM, especially a NM guarding a tenuous but huge empire inland to the west, and relations between the locals and the central government were less poor, I think the US would have had to send a lot more men toward Santa Fe and they'd have no easy walk to it, nor would managing to take it be the end of the story of Nuevo Mexico fighting.
Honestly, it would take more than camels alone to turn the tide--but the lack of consideration given this option OTL suggests to me it would take a deep POD to introduce the camels at all, and a policy doing so could well be an aspect of a far more astute New Spain administration that perhaps has learned to better incorporate the native peoples who dominated their far north. Perhaps such a New Spain would undertake light-handed but firm expansion northward in a far less desultory and late fashion, explore the great interior more fully, learn of mineral wealth to be mined there, set up suitable colonies in places like the Salt Lake area to support stronger forces as well as cultivating selected Native allies as a matter of course. Perhaps there would be no Pueblo Revolt and thus hiatus in Spanish power in New Mexico, perhaps a substantial and loyal population in California would secure their west flank long before it weakly attempted to OTL.
If any substantial Spanish expansion puts any significant number of Spanish-loyal persons in the Sacramento River valley, they will discover gold there; perhaps the kind of regime I am talking about can manage to maintain strong government control of the gold fields and thus manage to see to it that the incoming population is loyalist; meanwhile the gold itself is going to be a major thing for the Spanish state. A suitable policy to keep control probably involves the state having to wisely forgo attempting to confiscate all the gold to itself, permitting the lion's share of it to remain in the hands of the soldiers recruited to serve there--but these soldiers will have little better to do than to continue to serve, while staking claims to excellent land and using their fortunes (badly discounted by regional inflation locally of course) to import goods to the Bay Area, where their descendants can jump-start a major agricultural and urban area essentially purchased by all that private-hands gold, which is thus dispersed gradually onto world markets.
If meanwhile exploration, trade and missionizing of the interior assisted by camel transport has been going on, finds of more gold and silver in the interior can attract more population there, jump-starting regions like OTL northwest Nevada in the Washoe-Tahoe area as agricultural zones to feed dispersed mining populations, their output funneling to the Bay to sustain Bay Area California as a major developed center, with population meanwhile taking some very good farm and ranch land under cultivation.
