Page 106. " We pass by a marker saying something about Lewis and Clark. One of them came up this way on a side excursion from the Northwest Passage "

Meriwether Lewis (1774-1809) and William Clark (1770-1838) led an expedition from the Mississippi River to the Pacific coast, detailing topography, natural resources and Indian villages. As this was one of the earliest such expeditions, its findings were instrumental in the westward expansion of the USA 

Page 112. " There was a passage he had read and repeated to himself so many times it survives intact. "

Einstein photographed in 1921
Public DomainEinstein photographed in 1921 - Credit: Ferdinand Schmutzer
The passage in question comes from Albert Einstein's speech to the Berlin Physical Society in 1918, for Quantum Theory founder Max Planck's 60th Birthday.

The full text

Page 124. " The book states that there's a theoretic component of man's existence which is primarily Western "

The book Pirsig refers to is The Meeting of East and West by American philosopher and teacher F.S.C. Northrop. It presents the thesis that an 'undifferentiated aesthetic continuum' exists in the East whereas Western thought is informed more via rationalism. This means that a concept in the East will be understood by intuition, while in the West it will be understood by postulation. This difference relates directly to Pirsig's Romantic and Classical understanding respectively.