Brian, I am familiar with both trees and you have a Redlands White Sapote. Although the exterior of a June plum is similar to your fruit, june plums have a large spiny seed that reminds me of the seed pods produced by a sweetgum tree. The Redlands at my Dad's produces fruits exactly like what you have. The seeds are always abortive and fruits are small. I finally realized that it needs a pollenator and grafted some other varieties to the tree about a year ago. I think that will solve the issue. I got most if them from Kaz and they grafted easily.