The history of Silicon Valley now extends 70 years, encompassing multiple generations of hardware and software technology, of company founders and venture capitalists, of migrants both domestic and foreign, of tech evangelists and myth creators. And of an evolution, from a small electronics industry south of San Francisco into a global network, dominated by software-is-eating-the-world collossi with twin centers: the greater San Francisco Bay Area and Seattle.

Condensing this range of stories into a compact narrative isn’t a task for the timid, but Margaret O’Mara, a historian at the University of Washington, has pulled off the feat with panache in “The Code: Silicon Valley and the Remaking of America.” She distills voluminous monographs and biographies, newspaper articles and trade-industry publications, unpublished company materials and transcripts that she gleaned from various university archives into a briskly paced narrative. She also enlivens the book with the reflections of dozens of participants who played roles in the Valley early on, obtained through interviews she conducted and from oral histories collected by others.

The story begins in 1949, when, as Ms. O’Mara puts it, “the U.S. government got into the electronics business and became, in a sense, the Valley’s first, and perhaps its greatest, venture capitalist.” Or the start could be in 1952, when administrators at Stanford University began developing open space for a new kind of research park, giving corporate tenants special access to its faculty and students and encouraging entrepreneurial ventures that originated in the university’s labs.

Ms. O’Mara situates the story of information technology within the bigger picture of economic geography. Even in the early 1970s, she tells us, Northern California remained a “long shot” to become the center of the computerized universe. IBM, headquartered in upstate New York, reigned in corporate-land. Texas produced more microchips. Venture firms were mostly based east of the Mississippi.