FOSSIL HUNTING IN UTAH AND ARIZONA 



By CHARLES W. GILMORE 



Curator of Vertebrate Paleontology, U. S. National Museum 



The 1937 Smithsonian Paleontological Expedition for fossil verte- 

 brates had as its main objective the exploration of certain geological 

 formations that occurred on and around North Horn Mountain in 

 central Utah. This area had been brought to our attention by mem- 

 bers of the U. S. Geological Survey because of the fact that some 

 1,650 vertical feet of beds originally mapped as Wasatch, Eocene, 

 were later found to carry fragmentary dinosaur and mammalian fos- 

 sils. The hope of obtaining identifiable specimens that would accu- 

 rately date these deposits and also the hope of opening up a new field 

 for horned and other dinosaurian specimens were the motives which 

 actuated this undertaking. 



The party, consisting of Messrs. George F. Sternberg and George 

 B. Pearce under the direction of the writer, established camp at the 

 Olsen Ranch in " Joes Valley " in the Manti National Forest on 

 June 15. On the following day under the guidance of Dr. E. M. 

 Spieker, of Ohio State University, who had mapped the geology of 

 the region and was therefore conversant with all aspects of the field, 

 collecting was begun. 



On the very first day Pearce made the amazing discovery of an 

 articulated skeleton of a very large sauropodous dinosaur, a totally 

 unexpected find in an Upper Cretaceous formation in which also 

 occurred the remains of ceratopsian dinosaurs. Only once before has 

 such an association been found, and that in the San Juan Basin in 

 New Mexico, where Dr. John B. Reeside, Jr., in 1921 found the type 

 specimen of Almnosaiirus sanjuanensis Gilmore, which the present 

 specimen appears to resemble closely. Although subsequent study 

 may modify such a conclusion, the inference at present is that these 

 Utah deposits containing dinosaurian remains on North Horn Moun- 

 tain are equivalent in age to those in New Mexico. 



The Alamosaurus skeleton was found in a badland area at the south 

 end of North Horn Mountain. It was lying on its back with the 

 anterior part of the skeleton projecting from the outcrop. The head 

 and neck had long since been eroded away and destroyed. The dorsal 

 series, owing to its proximity to the surface, was so soft and disinte- 

 grated as to be valueless and therefore was not collected. The left 

 fore limb and foot in the articulated position as found (fig. 2) 

 measured 9 feet in length, which gives some idea of the great size of 



