the lava flow by the hardening of the surface of 

 the molten stream and the stiffening of its side 

 walls, while the liquid interior drains away leav- 

 ing an empty tunnel of varying diameter in 

 different flows. After the tube has formed, there 

 are portions of its roof which are unstable and 

 the collapse of a portion of the roof forms en- 

 trance to the tube, making a cave. Many such 

 caves collect winter snow and frozen moisture 

 to form "ice caves" in summer, a frequent 

 source of water supply. Collapse of different 

 parts of the roof of a tube may leave a narrow 

 segment which forms a "natural bridge." 



Lava Bombs — Tree Molds — 

 Pit Craters— Water Holes 



Among the curious lava features are the 

 "bombs" which are scattered about the cinder 

 and spatter cones, where the sputtering lavas 

 have ejected blobs of magma varying in size 

 from a quarter of an inch to several feet, and 

 which hardened sufficiently while in the air to 

 retain a globular tear drop, or spindle shape. 

 Some of them have slender tails which are often 

 partially broken away. 



Tree molds are really lava casts of the trunks 

 and roots of trees. They were formed by hot 

 lavas flowing about the trunks of existing trees, 

 cooling and hardening sufficiently upon contact 

 with the moist wood so that the "mold," in the 

 form of a cylindrical cavity, remained as the 

 tree was completely consumed by the heat. 



Pit-craters are common along the Great Rift, 

 where subsidence of the lava after a period of 

 flow has caused portions of the surface to col- 

 lapse, leaving crater-like depressions. It is in 

 these depressions that clear, cold water is often 

 found. Most of such water is undoubtedly the 

 result of melting snow and ice accumulations of 

 winter in the ice caves and interstices of the 

 very much broken lava flows. In many water 

 holes, there is sufficient flow through the sub- 

 terranean seepageways to keep the water cold 

 and refreshing upon even the hottest days of 

 summer. 



Flora — Fauna 



Contrary to general impression, a fair amount 

 of vegetation exists, principally upon the cinder 

 cones and cinder fields of the Great Rift. Limber 

 pines, aspens, and choke cherries reach tree size, 

 and shrubs such as mockorange, sage, bearmat, 

 and rabbitbrush are common. Many beautiful 

 flowers cover the cinder fields in season. The 

 usual birds and small animals found in western 

 semiarid areas exist in the monument, and deer 

 are sometimes seen. 



Indian Trails 



Following the Great Rift is an ancient Indian 

 trail which even today is readily discernible. 

 There are legends of the Indians' use of the 

 caves as safe strongholds and for transient 

 habitation, while at Indian Tunnel there are 

 perhaps 20 semicircular heaps of stones used to 

 anchor the windward sides of teepees against 

 the prevailing winds. Arrowheads and spear- 

 heads are sometimes found. 



Facilities 



Adequate camping space is provided at the 

 monument, and a limited number of tourist 

 cabins, with provision for meal service, are 

 available during the season. A loop road south- 

 ward along a portion of the Great Rift provides 

 access to many points of interest. 



A dministration 



Craters of the Moon National Monument is 

 one of the areas owned by the people of the 

 United States and administered for them by the 

 National Park Service of the Department of the 

 Interior. In these areas the scenery and the 

 objects of historic, prehistoric, and scientific 

 interest are carefully preserved and displayed 

 for public enjoyment. 



This monument is in immediate charge of a 

 custodian, and communications regarding it 

 should be addressed to the Custodian, Craters 

 of the Moon National Monument, Arco, Idaho. 



NORTHWEST PORTION OF 



CRATERS OF THE MOON NATIONAL MONUMENT 



IDAHO 



Corrected February 1943 



Revised 1947 



U. S. Government Printing Office: O-F-761251 



r 1 raters 



of the Moon 



NATIONAL MONUMENT 



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