I wouldn't cut the canes down at this point, because if this is a once-bloomer, you will remove all hope of bloom this spring. You could cut it back some, but you need to retain that old wood.

There are multiple possibilities as to identification -- anywhere from an old rambler to -- rootstock. If it is rootstock, you will know when you see spring bloom, which will only appear on old wood.

Can you get photographs of some of the foliage?

What would be really helpful is if you could pull an entire leaf off of the cane, including the stipule and all of the leaflets -- lay it on some paper, or bricks or something, and take photos of both sides. Something like the photo attached (but show both the top side, and the underside.

Rain! LUCKY YOU!

Jeri In Dry SoCal

Jeri is right, as usual. Don't prune it until we can figure out who/what it is. In addition to sending in pics of the foliage, please do do send in lots of pics when it blooms next Spring (you might give it some food now, also).

It will obviously be OK for water until Spring. Once we can see the blooms and also some pics of the overall plant, I'm sure someone on here can tell you at least what kind of rose it is, and then you will get detailed instructions as to how to prune it. But - leave it alone for now, except for some food. It may not have bloomed much because it was covered with other stuff, and not getting enough light. It should bloom this coming Spring.

Jackie

Thanks for your responses. Sorry it took me a while to follow up.
In the original post I used the word "rootstock" perhaps too casually. What I meant is that there's a thick, woody log-looking vine along the ground, from which the canes are sprouting. Two of those canes are green, two are woody. All are sprouting out long vines that are green, and covered with leaves at the end. Bear in mind that they are long and leggy like this because before I cleared the way they had been both covered by brambles and climbing up into a tree.
One more possibly useful piece of information is that this thick stock is planted next to an active climber that's very common in my area, one with countless little (2 1/2-inch diameter), light pink roses with many petals. Can't remember the name but I would recognize it.
I'll post the a photo of the base/rootstock (?) here, and in two more posts a photo of the leaves and of the whole deal. (The site will allow me to post only one photo at a time.)
Would appreciate your advice after seeing these images.

Oops. Posted leaves with the previous. Here are the canes coming out of the base.

And this is looking back over the long vines and leaves to the canes (curving at top of photo) to the base root/log thing.

Veilchenblau?

Unfortunately mine died many years ago.

The Help-Me-Find link is below.

Here is a link that might be useful: Help-Me-Find link.

Thanks for the guess. It can't be that one because it has terrible thorns all over. It has been entwined with blackberries, and I've confused their dead growth because their thorns are similarly nasty. The ones on the old, woody canes are big like cat claws.

Another possibility is that when it had purple flowers it was Veilchenblau, but now that it is not blooming it is just understock

I'm no good at comparing leaves, etc. But maybe Queen of the Prairies? (I grow her).

http://www.helpmefind.com/rose/l.php?l=21.145408

Check out the other pics, too.

If so, she'll have massive, frightening base canes with enormous thorns and then thinner, floppy stuff up tall. The thorns get smaller as you go up. I have one climbing my large shed :)

Here is a link that might be useful: HMF QotP