OEEGOX SHORT LINE OGDEX TO YELLOWSTONE. 



121 



A place of more than local interest is Lava Hot Springs, in Port- 

 neuf Canyon 12 miles east of McCammon, where in 1914 the State of 

 Idaho built a natatorium inclosing a concrete swimming pool 33 hj 

 66 feet for puhhc use. A number of hot springs issue from the bank 

 of the river, and hear them is a popular camping place. In the can- 

 yon at and above the hot springs there is considerable calcareous 

 tufa, a soft cellular limestone deposited by the evaporation of water 



carrying lime in solution. 



The gently sloping benches or terraces from McCammon to the foot 

 of the mountains on the east and west are composed of outwash 

 material which, though deposited by momitain torrents, has never- 

 theless accumulated so gradually that it makes a good soil. Lai^e 

 quantities of grain are raised on it by dry fanning. The great Vvhite 

 ledge seen on the mountain side 5 miles east of the village is a band of 

 gray sandy limestone about 100 feet thick. The Harkness ranch, 

 just north of the village, was one of the first in tliis region and was a 

 common stopping point for freighters before the raiboad was built. 



[\intame 



o 



point.i Water power at McCamm 



tlie local gris 



and 



electric-light plant. 



leaving McCammon the train runs down 



nrtd for R number of miles 



top of the lava into a little canyon, and for a number of 



the river and the edge of the lava. Toward the north the lava wall 



most 



increases from 10 to ou leei ui neigui. j-h uausv ^-lav^^o x.^ c.^.^... .^^^ 

 is well exposed, but the lower part is concealed by large and small 



from 



forces. Fme exposures of black columnar basalt =^ are a lmost con- 



LI ■ I 1^ II II ^^^^^ ^ m^^^^^ tm ^^^^^ 



1 Measurements of the flow of Portneuf 

 River sliow a mean discharge of 265 

 second-feet at Topaz, a Nation in the 

 canyon east of McCammon, during 1913-14 



1S97-1S99 and 1912-1914. 



unng 



The records at 



Pocatello show from a minimum flow of 

 14 to a maximum flow of 1,880 fcecond- 

 feet. No large power plants are feasible 



on this stream. 



2 Columnar structure, or the di^Tsion of 

 a rock into prisms more or less straight 

 and parallel to one another, is a common 

 feature of basalts. Well-known examples 

 of this structure are the Giants Causeway 

 and Fingab Cave, in Ireland; the lavas 



and the valley of the Columbia in Oregon. 

 Asin the drying of a mud puddle cracks 

 break the surface into figures ha^'ing five 

 or six sides, so in the cooling of molten 

 basalt the prismatic slirinkage cracks 

 start at right angles to the cooling sui'face. 

 If the rock were perfectly homc^eneous 

 and the cooling uniform, the columns 

 would all be hexagonal and of uniform 

 thickness. The slower the mas^s cools and 



o 



will 



and 



as the upper and lower siuiaces of a 



are 



find 



upper portion. As the 

 eloped at a right angl 



umns t 



^olumns 



in thP iuvergne/in central France; the , veloped at a right angle to me cuux..^ 

 PaWles of the Hudson; the Watchung ' surface it follows that a sag or depression 

 r'^'::":^-' J '„.n,„„ ' A^ T-n.Hth« in the surface of a basalt sheet IS underlain 



Mountains, west of Orange, N. J.; and the 



Snake 



bv radiate columnar structure. 



