Hill chose to build his railroad north of the competing Northern Pacific line, which had reached the Pacific Northwest over much more difficult terrain with more bridges, steeper grades, and tunnelling. Hill did much of the route planning himself, travelling over proposed routes on horseback. The key to the Great Northern line was Hill's use of the previously unmapped Marias Pass. The pass had initially been described by Lewis and Clark in 1805, but no one since had been able to find it so Hill hired Santiago Jameson to search it out. Jameson discovered the pass 1889 and it shortened the Great Northern's route by almost one hundred miles. The pass had been discovered by John Frank Stevens, principal engineer of the Great Northern Railway, in December 1889, and offered an easier route across the Rockies than that taken by the Northern Pacific.