The one on the left looks like a polyphemus moth caterpillar (https://webdoc.agsci.colostate.edu/bspm/arthropodsofcolorado/Polyphemus-Moth-September-2.pdf), while the one on the right looks like a forest tent caterpillar.

Thanks, I appreciate your help, The Polyphemus moth caterpillar looks just like my picture. I looked for tent caterpillar moth pictures, and checked western forest tent caterpillars, and couldn't find a good match, as my photo has clustered bristles that I didn't see on the forest tent caterpillar photos. Do you have any other ideas on it? And how does one even go about identifying caterpillars? (I am writing a nature blog and doing some social media associated with it, and this month am featuring caterpillars, so I'm hoping to name the species correctly. I see you're an entomologist, you might find it worth a laugh or smile, at least. www.landexplained.com)

I still think that it's a Malacosoma sp (tent caterpillars).  There are several species.  How about M. tigris, the Sonoran tent caterpillar?