Ethan,
Some quick thoughts without getting out my reference material. And tomorrow I'm leaving on a 10-day trip that I have to get ready for.
Natural Soda Products is the facility south of Keeler. Inyo Development was located north of Keeler on the lake (west) side of the railroad. Inyo had evaporation basins both north and south of Keeler.
There are photos of both facilities located as such places as Eastern California Museum in Independence. Some images from its overall collection are on-line; but, I cannot recall exactly what is available there. Other sources would be CSRM photo collection. There are some maps of Keeler in the collection of Nevada Historical Society in Reno.
I have scans of some of the SP valuation maps. There are three of the Keeler area and I can post probably post PDF versions this evening.
Brian Norden