your cacti looks like a cholla, do a google search, these are very hardy plants. these, along with opuntias look like shriveled masses, but come spring... woooweeee, there beautiful. i hope this helped. if you want to do something to help them tho, you can put protection on it, incase it snows

This looks very much like frost damage in an advanced stage. Few things you can do now, but once the dead parts can be identified you should cut these away.

Pieter

Your photo is too dark & unclear. When I lightened it & enlarged it, & you appear to have a dead base, but have plenty of cuttings to work with. If the base is black & soft, it is probably dead. Sometimes things sprout from material that appears to be dead, but it is likely not viable. Take the cuttings at the nodes, let them dry, & plant in a dry media.
It may be an Argentinean cactus, but it is hard to tell from the picture. It could be a cholla, but most people do not landscape with cholla. If it was professionally landscaped, get good pictures of those other plants so you can get some good advice on them. You may have some valuable plants that merit saving. Get a larger picture of the cactus with clear spines & try & ID it again.
The cacti were probably mature specimens that normally did well in your climate. I protect my valuable cacti from rare frosts, but I lost a few plants this winter due to an unusual prolonged cold spell. I use burlap, keeping it away from the spines. Many growers in my area had burned plants &/or were scrambling to protect them this winter due to an unusual cold snap. It is frustrating.
Do a search for key word frost on the CA or NV forum & you might get some tips on frost protection.

I would wait a bit before pruning. I have a cholla (Opuntia imbricata) in my cacti garden outside and this looks like mine after the winter. But every year it perks up and starts growing. It's almost 4 ft now. And this is zone 5 Milwaukee...much colder and wetter than you I think. So give it a chance first.

Dave
Milwaukee