We rumbled over the plains and valleys, climbed the Sierras to the clouds, and looked down upon summer-clad California. And I will remark here, in passing, that all scenery in California requires distance to give it its highest charm.

Chapter 54 from Roughing It:

Chapter 52 of Roughing It:

"Six months after my entry into journalism the grand “flush times” of Silverland began, and they continued with unabated splendor for three years. All difficulty about filling up the “local department” ceased, and the only trouble now was how to make the lengthened columns hold the world of incidents and happenings that came to our literary net every day.

From Explanatory Notes:  Clemens returned to New York “in an express train ... a distance of nearly twelve hundred miles by the route I came,”  He stays at the Westminster Hotel.

Mark Twain explained, in another Alta dispatch, that on 17 March he had been asked to “make a few remarks” to a Sunday school, and that he “told that admiring multitude all about Jim Smiley’s Jumping Frog,” which in turn led to a more formal invitation. “I did not intend to lecture in St. Louis, but I got a call to do something of that kind for the benefit of a Sunday School.” 

Railroads from New York to St. Louis, 1867:

Scharnhorst ( The Life of Mark Twain: The Early Years, 1835-1871, page 383) has Twain entering St. Louis after a transfer of trains in Terre Haute.   These seems unlikely as the only line to East St. Louis from the east in 1867 was the Ohio and Mississippi.  The Indianapolis and St. Louis was the second line to reach St. Louis and it was not completed until 1870.

On the point of departing San Francisco and a return to New York, Twain in his farewell to the west coast offered an image of what he thought the future would bring. It also provides a window on his view of the industrialization occurring in the world around him.  From his impromptu farewell address to San Francisco:

Flora (sternwheel steamer): The ship was built for the company's trade with Marysville, and thus had an exceptionally shallow draft of 11 inches. She was launched in 1865 then acquired by the California Pacific Railroad Company in 1871.

From Sacramento, "They steamed inland on the Flora to Marysville on the Feather River..."  (pg 356 Scharnhorst V1)

From Marysville,  "They then took a stage to Grass Valley..." 

Scharhorst reports that Twain spent the night in Meadow Lake, a mining camp  where Orion had previously lived.  It is currently a ghost town on the map called Summit City.