+ This is a spot where I am not likely to be very particular about what grows.
- It looks like this was a volunteer with how close it is to the retaining wall.
The Ash (Fraxinus sp.) in the corner is a young-mature tree with a single trunk DBH 11". Live crown ratio is around 50%.
New foliage looks healthy. No significant signs of decay.
Residential site, northern aspect, shrub border with no regular irrigation. No signs of recent site disturbance, no paving, fill, or grade work in the dripline. Slope grade is flat. Exposed to prevailing West winds. Half the dripline is under a foot or more of soil behind a retaining wall that looks to predate the tree.
Fence, retaining wall, landscape plants, garage.
No signs of root rot, exposed roots, or root pruning. Crown defects: moderate co-dominant leaders. Presumably the roots have made it under the retaining wall and established some anchor on the far side.
Part most likely to fail: co-dominant leader. Moderate failure potential on moderate parts with limited targets for a hazard rating of 2+2+1 = 5.
Monitor tree. Consider bracing or cabling with 3/8 inch common grade cable. Rationale: While this tree isn't in an ideal location it is established, comely, and not really likely to do much harm. There is some cracking in the retaining wall that should be monitored.
Some pruning should be done to establish a dominant leader.