200 University of California Puhlications in Botany [Vol. 7 



grow in varying degrees of density over most of the valley bottom 

 except wliore farming operations have interferred. An estimate based 

 upon a hurried visit in 1918 and upon data supplied by Forest Ranger 

 George Parke places the total amount of rubber at 2,280,000 pounds. 

 Extensive areas of Rabbit-brush have been located in the vicinity 

 of Mono Lake, but our analyses indicate that it is not so rich as that 

 from Owens Valley and Benton. The principal varieties represented 

 are viridulus and consimilis. There are about ten square miles of 

 fairly large plants to the north and northeast of the lake in a nearly 

 pure stand. On the south and southwest sides it is mixed with Sage- 

 brush over an area of perhaps sixteen square miles. In Adobe Valley, 

 which lies southeast of the lake, we find it in good formation from the 

 Adobe Hills to the River Spring Ranch and in a narrower belt as far 

 as Dutch Pete's while there are perhaps a thousand acres of it in a 

 belt extending from Gaspipe to Indian Spring. By using the methods 

 indicated above, we have estimated that these areas centering around 

 ]\Iono Lake would yield about 700,000 pounds of rubber. 



The estimated total amount of rubber obtainable from District 1 is 

 3,280,000 pounds. 



1). DISTRICT 2— MOJAVE DESERT, CALIFORNIA 



This might almost as well be called the "Antelope Valley District" 

 since it centers around this westerly arm of the Mojave Desert. It is 

 not very promising as a rubber producer because of the large number 

 of varieties represented and the consequent fluctiiation in rubber con- 

 tent. The largest continuous area of shrub is a belt of gnaphalodes 

 about two miles wide and perhaps thirty miles long, which extends 

 diagonall}' across the valley in a northwesterly direction from near 

 Palmdale to a point west of Rosamond. The shrubs are below medium 

 size, the woody portion weighing on the average about three pounds, 

 and there are about 50,000 plants per square mile. A similar belt is 

 reported still farther west. These belts are undoubtedly due in large 

 part to the burning off or clearing of the Sage-brush in the remote 

 past and represent one stage, in the succession whicli will ultimately 

 bring this Sage-brush back as the dominant climax species. Analyses 

 indicate that this shrub carries an average of two per cent of rubber. 

 Smaller areas of gnaphalodes are scattered all around the borders of 

 Antelope Valley and even to Tehachapi Pass and northward to Owens 

 Lake, mixing slightly along its upper limits with moliavensis, but the 

 lower, more alkaline lands support a scattered growth of what ap- 



