I was able to find a copy of Nancy's original pattern here and an even older pattern, entitled Rose Album, from the Ladies Art Company here. The latter pattern is pieced while Nancy's pattern is an applique pattern.
I really like the look of this block but it is not an easy one and I'm not really sure how I would put it together. I decided not to try to make a 6" block for my sampler. I do hope to attempt a larger size at some point though. If you've made this block, please let me know how!
The California Rose block can be found in Electric Quilt's Blockbase program as #3651.
There are a couple of California Rose quilts here and here that have very different looks.
This is how Nancy's version might look-