1914] Loughridge: Kumus and Nitrogemn Calif ornia Soil Columns 235 



A column from Riverside was taken from. Arlington Heights 

 orchard lands on the south, with the assistance of Mr. J. H. 

 Reed, and we were able to reach a depth of eighteen feet with 

 comparative ease. 



Another mesa soil column was taken by Mr. F. E. Johnson 

 from nearly one mile south of the town of Corona, and is a good 

 representative of the orchard land of that vicinity. A depth of 

 twelve feet was reached with difficulty because of the presence 

 of much gravel. 



The red mesa land on the south side of the valley also con- 

 tains very low percentages of humus and of nitrogen. This is 

 especially true of the Riverside soil, more than one-half of whose 

 supply is in the upper two feet. Its nitrogen is also very low. 

 The Corona soil is somewhat richer in nitrogen, but in both soils 

 and doubtless on the rest of the mesa, the need of good green- 

 manure crops for the production of humus is very apparent. 



Los Angeles Alluvial Plain. — The three rivers, Los Angeles, 

 San Gabriel, and Santa Ana, have each brought down from the 

 San Bernardino Mountains large quantities of silt, sand and 

 clay and formed a large body or region of alluvial lands known 

 as the Los Angeles alluvial plains. Each river preserves its 

 own course through these plains and has built up its own alluvial 

 plain with its own material independently of the others. We 

 thus find that the soils of the San Gabriel are of a more sandy 

 nature than those of the Santa Ana, probably because of the 

 more rapid velocity of the river current over a shorter distance ; 

 the Santa Ana leaves the mountains east of San Bernardino and 

 flows by a circuitous route along the southern side of the valley 

 and thus seems to have left much of its coarse material behind 

 and deposited chiefly clays and silts in the alluvial plain. 



The San Gabriel Plain is represented by three columns. One 

 was taken from the place of Dr. S. S. Twombly, south of Fuller- 

 ton, to a depth of ten feet; another from the place of Mr. J. B. 

 Neff, near Anaheim; while the third column was taken a mile 

 south of Compton. 



The land of that plain belonging to the San Gabriel and 

 especially between this and the Santa Ana River is greatly varied 

 in character, as is indicated by these three columns. In some 



