332 RURAL CALIFORNIA 



where the frost penetrates deeply into the ground 

 and nowhere in California has concrete been laid un- 

 der such conditions." In high mountain districts 

 different and more expensive construction is em- 

 ployed but perhaps nine-tenths of California high- 

 ways will be constructed in valleys and foothills 

 where ground freezing is infrequent and then only 

 superficial. 



Although the specifications have made good against 

 such freezing as the valleys and foothills receive, re- 

 cent experience indicates that a thicker base may be 

 necessary to enable the roads to carry the heavy 

 weights of freighting trucks, which were not fore- 

 seen when the roads were built. Since truck-haul- 

 ing has been resorted to to fill the lack of transporta- 

 tion caused by the war duties and deprivations of the 

 railways, there has been injury done to the cement 

 highways which may require heavier construction. 

 The roads were planned for much lighter traffic than 

 they have recently carried. In view of this fact it 

 is significant that the Bureau of Public Eoads of the 

 United States Department of Agriculture reported 

 in May 1921 that 87J per cent of the main concrete 

 highways of the State (1262 miles) were in good 

 condition. Even if additional expense should be re- 

 quired to render greater service to industrial trans- 

 portation., California still enjoys an advantage in 

 highway construction in the fact that all materials 

 employed are abundantly produced not only within 

 the State but at several distributed points. Suitable 

 rock and cheap power for crushing are widely avail- 



