208 VnivtrsUy of Califoriiiu I'lihlications in llolatiu l^'"'-" 



According to Professor Jones, the avernge wciglit of Utali plants, 

 after cntting off tlie twigs, is about fifteen pounds, but in ordei- to be 

 pci-fcetly safe \v<' have taken only t<'ii pounds as the weight in uiaking 

 up oui" estimates. 



Fi'om the dala indicated ;d)Ove and taking 1.12 per cent as the 

 jiverage eonlent. we estimate tlie total amount of rubber present in 

 ('liri/sofhanDius in t'tah to be not less than 20,000,000 pounds. 



(J. DISTRICT 7— (COLORADO 



Our explorations in this state luive been far from exhaustive, con- 

 sisting Duly of one visit to the northwestern part, a north-and-south 

 journey along the easterly base of the Rocky Mountains, a visit to the 

 San Luis Valley, and notes and samples taken along the line of the 

 Denver & Rio Grande Railroad. The only important area of (lirijso- 

 thamnus that we have located is in the San Luis Valley of south cen- 

 tral Colorado, where we estimate, from observation and from rei)oi-ts 

 of reliable residents, that not less than S()(),000 acres are fairly well 

 covered with (Uiri/sofliamii us of the pinifolins variety. Over much of 

 this area the plants stand about ten feet apart, that is, tliere are about 

 four hundred and thirty-five i)lants to the acre. Since Grease-wood, 

 or Cliico {Sarco'batus vermicid'atus) and other impurities occur in 

 some portions of the valley, we have taken only one-half of this 

 number as a basis for estimates. The plants are of medium size, the 

 average weight after the removal of the non-rubber-bearing jiortions 

 being perhaps five pounds. Two samples taken at Alamosa yielded 

 3.41 per cent and 1.11 per cent, respectively. A third, sent fr(mi near 

 Center by Mr. Wm. 0. Sander, analyzed 3.59 per cent. This makes an 

 average of 2.70 per cent of pure rubber. On this basis the total amount 

 of rubber present in this one valley would l)e about 24, 300, 000 pounds. 

 This is probably the largest single body of shrub in Colorado, if not 

 in the whole West. Smaller but otherwise siinilar areas doid)tless occur 

 in some of tlie unvisited river valleys of the southwestern i^u't of the 

 state. ^'^ Along the Gunnison we found only small detached areas of 

 Rabbit-brush and the same is true of the valley of the Yam[)a, in north- 

 western Colorado. 



The most easterly stations at which we have found rubbei'-bearing 

 shndis lie along the east base of the liockx' ^iountains from Fort Col- 

 lins and Denvei' to Trinidad. Five samples of grovcoJnia from these 



1" See }>. ISO. footiioto, 



