Some addendums to the corrections – it never pays to be overenthusiastic.
Page 27, photo caption:
"This is a Howe truss bridge across river at eagle gap."
This is another of A. A. Hart's original photographs #274 which was originally captioned "Bridge at Eagle Gap". The bridge is more accurately described as a "Burr Truss bridge" because of the arch through the members.
Actually, I'd describe this bridge as a Howe truss reinforced with a Burr arch. Burr's truss design was quite different.
Burr patent x2769, 1817
Howe patents 1685, 1840; 1711, 1840, reissued re175, 1850; 4726, 1846 (this one most significant)
Page 58, paragraph 3:
"On August 9  the first rail laid west of the Missouri [River] and the first in California was laid."
There were at least two railroads in California with iron rails before 1855. A contractors railroad in San Francisco even provided California's first railroad fatality in July 1851 with one S. Mellison crushed between a trains iron wheels and the iron rail. In 1853 a mining railroad with iron rail hauled ore from Virginia Hill to Auburn Ravine in Placer County. However, it is worth noting that both of these early lines were animal powered and not steam powered – and that they might more commonly be described as 'tramway" rather than railways. Also not mentioned is the Arcata & Mad River, incorporated as the Union Wharf and Plank Walk Company on Dec. 15, 1854 with a horse-powered common carrier wood rail line, which is commonly considered to be the first railroad in California (although clearly not the first used of railed vehicles).
Page 69, paragraph 1:
"[Theodore D.] Judah, the man who built the suspension bridge at Niagara Falls"
Theodore D. Judah was the Chief Engineer of the Niagara Gorge railroad which ran from Niagara Falls to Lewiston. The Niagara falls suspension bridge was designed and built in 1853 by John A. Roebling, who later built the Brooklyn Bridge.
If we are to be picky, the Brooklyn Bridge was designed by John Roebling, and construction started before John's untimely death. It was largely finished under his son, Washington A. Roebling, with able assistance by Washington's wife, Emily, who served as his eyes, ears and mouth on the job when Washington was laid up for an extended period with the bends during much of the construction.