Who is Johnson? How does he rate a field?
Oh, I looked, but I did not find. Much. Besides repeated mentions of Johnson Field ("an inactive spreading basin...used for passive recreational uses"), I found nothing but this interesting LA times article from 1992. The article discusses early plans for Hahamongna Watershed Park and a disagreement about putting soccer fields there. At the end there's a brief mention of Johnson field: "a small baseball field built by city employees for a municipal soccer league." I think he meant it was originally built as a soccer field but by the time of the article it was used more as a baseball field.
The article said all parties agreed the field should be eliminated. It's still there, after a fashion, although they finally stopped watering it this year. Makes sense. Drought + rarely used field - water = savings (or at least common sense).
So I found out that much. But I still don't know who Johnson is, or how he rates a field. Or a rock, for that matter.