Owl: glad to be useful. You may have gathered that I am a total nature nerd!
Sunflower: if your rose was flowering normally until this year, probably a virus, yes. There are some chemicals that will do similar, but I don't suppose you've been feeding your rose growth hormones or synthetic dyes? In roses the condition is generally spread by aphids or flower thrips. Keeping those down, either with soapy water, physically rubbing them off if it's a small bush, or encouraging ladybirds and lacewings to come and eat them, should help. Some departments of Agriculture will actually sell you little packages of predatory insects (or their eggs, depending on time of year). Is that a thing in America?
If it's a small bush and hasn't been infected for too long, there are things you can try. Prune your rose heavily, taking out all the obviously infected areas and a few inches below them,until the tissue looks healthy. Don't worry, roses can take very hard pruning, and are generally the better for it. Take the opportunity to shape your rosebush, opening the centre up for better airflow and cutting the outer stems so the top remaining bud on each stem is facing outward. Good airflow through the bush prevents a lot of the fungal diseases that afflict roses. Cut the stems at a slight slant, not flat, so water will run off the ends easily (fungal disease prevention again).
Don't compost the pruned-off wood or leave it lying about. Gather the prunings and dispose of them by burning, or in a sealed parcel in the rubbish, so as not to reinfect your plants if some sapsucker decides to make a meal off the wilting branches. If your bush has not yet gone dormant for winter, give it a good deep watering, keeping the water off the leaves (that's a good rule anyway- roses are martyrs to fungal infections, and dampness encourages fungal spores). In any case, topdress the pot with some nice rich soil and a light mulch, then water it with dilute seaweed concentrate (can you get Seasol or equivalent in California?).
As a general rule, roses live longer and flower better if they are not overwatered or overfertilised. Soft sappy growth encourages sapsucking pests and the diseases they carry, and makes for leafy rosebushes with fewer flowers.
Whew! Sorry about the wall of text, but I hope it's useful!