There could easily be a a sustained population of feral cameos in the American southwest. It’s really just chance that we don’t have them today.
IOTL the US created an experimental camel corps just before the Civil War, but it was disbanded due to the outbreak of the war. The camels were simply turned loose and some established themselves in the deserts of the southwest, though others were caught during the war and ended up in various hands. The camel experiment was never revived after the war, but small numbers were imported commercially which meant there was a small supply of escaped and abandoned camels that mingled with the feral population. This population never grew large enough to become fully self-sustaining, but it lasted several decades with the last sightings in 1890.
Railroads were what really put the kibosh on camel usage. The post-war era was the great railroad boom, so rail filled most of the role camels were suited to in terms of connecting the arid and mountainous regions that were inhospitable to horse and oxen based transport.
So, if we imagine that someone had successfully imported camels a decade or two earlier* they would have had a much longer period for their usage to become more widespread and accepted. This would in turn mean a much larger population ( from both reproduction and import). I think that’s enough to get a self-sustaining feral population of camels throughout the region. Camels reportedly had no difficulty surviving in the area, which isn’t a surprise, and given how rugged and remote it can be I don’t think it would be feasible to remove them, even in modern times. The US-Mexico border would also complicate that. Plus, with enough time, I think the camels would come to be seen as a symbol of the west, just like the mustangs.
*IIRC the first proposals to import camels date to the beginning of the Mexican-American war to equip the expeditions from Texas to California. In reality it took a decade from those first proposals for the federal government to actually purchase camels, but there’s no reason they couldn’t have done it earlier if the idea was put persuasively enough. It really did make sense for the conditions. Or maybe an enterprising individual or company could have obtained camels privately to equip their own activities.