..I would say that's a symptom of Magnesium deficiency. Here we would either foliar feed or sprinkle about 1 oz of Epsom Salts around the base of the plant...

But you might want to do a soils test. I was told years ago to add epsom salts -- come to find out, with MY soil/water, that was the absolute worst thing we could have done.

Your other new foliage looks GREAT.

Weather is warming up and so is the soil. Yellow lower leaves in January isn't really a problem for the low desert. The leaves on the trees are falling, too. We have winter, then fall, then spring all within about a month. Wait to feed your roses until mid-February and add any Epsom Salts or alfalfa pellets in April when the roses are actively putting out blooms.

When I have pulled up a rose bush that had established a root system, and planted it somewhere else, I have noticed the leaves tend to turn yellow, at least until the rose has time to establish itself in the ground again.

Thanks Moroseaz!
That makes sense. Should I trim those leaves off?
The rest of the plants do look very good I think and they are blooming like crazy right now..
They are babies so I wasn't going to do much in the way of a January hard prune. Is that right?

Pull the lower leaves off or let them drop naturally. Some bushes will lose their lower leaves 1-2 times a year as the leaf ages out. In summer, it can cause problems with sunburn, so it's important to keep your roses healthy with regular water, regular fertilization during active leaf and bud season and good mulching to retard weed growth (root competition) and retain soil moisture and reduce soil temps. Gravel is not good rose mulch. Looks like you're using wood chips.

You say these are 'babies'. Did you add any soil amendments when you planted them? In the low desert we recommend adding 1/2 cup each bone meal and soil sulfur in the hole before planting. We do not add gypsum as we already have plenty of calcium in our soils. Phosphate and sulfur don't break down readily and need to be in the root area to be effective. During the spring, about April 10th, add a tbls of chelated iron (recommend Kerex) and 1/2 cup Epsom Salts. Water thoroughly before and after application. Iron and Magnesium Sulfate (Epsom Salts) are also in short supply in our local soils.

Unless you are gardening in an area that receives flood irrigation, these amendments are pretty much standard requirements for good roses. If you're gardening in an older section of the Valley that receives flood irrigation, you can probably dispense with the soil sulfur and maybe even the Epsom Salts. These areas may even have somewhat acidic soils after all these years. The rest of us have alkaline clay with hard, alkaline water and rocks that aren't rocks but calcium-rich clay hardened into caliche (adobe bricks).