SAN JOSE, Calif. (KGO) -- If you go to the Central Valley, there is a flurry of construction activity underway in and around Fresno for California's new high speed rail line.A 4,700 foot viaduct is under construction that will route the trains over Union Pacific Railroad tracks and the San Joaquin River into Fresno. Altogether, 119 miles of Central Valley construction is in progress as the rail authority eyes the first passenger service to link Silicon Valley with the Central Valley.In Silicon Valley, work is now starting on geotechnical analysis of proposed track alignments in Santa Clara County and in the City of San Jose.A crew on President's Day was busy drilling for core samples along busy Monterey Road, just south of Senter Road. The samples will help planners to understand soil conditions before proceeding with advanced engineering and environmental work.The High Speed Rail Authority says this is the same process that was done in the Fresno area before construction got underway there. It may be another year or two before a final choice of the rail alignment is made.Environmental impact reviews and land acquisition must also be done before any final decisions are made.The rigs are expected to drill at about 50 sites in Santa Clara County. The crews started their work last month and will wrap up in April. Temporary lane closures may be necessary with the rigs working along roadway shoulders and some time in landscaped median strips.