Q.What Is Happening To My Yucca?
Since planting my yucca, it’s leaves have gone from being very happy looking, strong and flat to the bottom foliage turning brown and dying off, but more noticeable, the leaves are curling up or folding in half. The plant seems to be unhappy. It gets full sun most of the day and in what I think is well-drained soil. I have been watering once a week. The location is in the hills of Los Angeles.

Certified GKH Gardening Expert
It is being overwatered. They are very drought tolerant, and will not tolerate wet soils very well.
Make sure that the soil has a chance to dry out, thoroughly, down to about 4 or 5 inches between watering. This will not be on a schedule, and will depend on the weather at the time.
You may need a meter to determine when you should be watering, but you should not have to water at all, even during drought.
This article will help you to care for them: