Nice article and photo, Susan. Erosion is a problem in California. I see it all around me. From the natural erosion by the ocean waves to the suburban housing tract mudslides from poor planning, the earth just moves all the time here in Southern California.
The state always seems to be shoring up hillsides along freeways. Expensive homes teeter on unsteady soil.
Grasses help anchor the soil but they are so shallow rooted that they only prevent surface erosion and not the underlying deeper movement.
It makes me think of an old children's song: "The wise man built his house upon a rock." "The foolish man built his house upon the sand and the house came tumbling down."
Can't help but have sympathy for the homeowner who bought a house in a suburban neighborhood. We obviously trust the contractor and developer to know what they're doing when selecting and grading the plots.
Many homes here have sloped yards and I love your solutions, especially the avocado tree.