Well fortunately bearded iris don't need all the mulch and prep that the water iris require. And yours have already proven to be adaptable to your rocky soil. As long as they have soil that drains well and a feeding of fertilizer a month or so before bloom and again during the dormant period they will probably be happy. The most basic of fertilizer is to use 8-10-10 or good old bone meal. Spread it around the plant so the roots get fed, but don't let it get on the rhizome because it can cause the rhizome to rot.
Your climate is less humid than here, so I am guessing you have hot days and cool nights? You should be able to transplant the iris in late August. I don't think you want to wait until September if it starts getting very cold at night. You need time for the roots to establish themselves before any frost. If you want to help out your roses now, you can always dig up the iris if blooming has ended and either put them in a new space or in pots until you have a new home for them ready. It is not ideal, but .....
Did they bloom at the top of your slope? if so, you could always put them back in that area if you don't mind their shorter height.
I know there are some other Cali iris folks in this forum that could give you some good feedback too.
