The Tehachapi Pass Railroad Line includes the world-famous Tehachapi Loop about halfway up the grade to Tehachapi Pass. Averaging a 2.2 percent gradient over 28 miles, the steep line was the crowning achievement of Southern Pacific Railway Company civil engineer William Hood and became one of the seven wonders of the railroad world. Cut through solid and decomposed granite by up to 3000 Chinese laborers from Canton, China, using picks, shovels, horse-drawn carts, and blasting powder, the line climbs out of the San Joaquin Valley and through the Tehachapi Mountains with 18 tunnels, 10 bridges, and numerous water towers for steam locomotives. It was completed in less than 2 years under the leadership of chief of construction J.B. Harris as the last link in the first railroad line connecting San Francisco and Los Angeles. The line was a primary factor in the early growth of Los Angeles and California, and this essentially unchanged single-track route remains in constant use 122 years after completion, carrying an average of 36 freight trains each day.