Imagine a question and stream-of-consciousness explanation for which this is the answer: January 8 , 1863
Question: The Central Pacific broke ground on January 8, 1863. Due to the lack of transportation alternatives from the manufacturing centers on the east coast, virtually all of their tools and machinery including rails, railroad switches, railroad turntables, freight and passenger cars, and steam locomotives were transported first by train to east coast ports. They were then loaded on ships which either sailed around South America's (( Cape Horn), or offloaded the cargo at the Isthmus of Panama, where it was sent across via paddle steamer and the Panama Railroad. The Panama Railroad gauge was 5 ft (1524 mm), which was incompatible with the 4 ft 8 1 ⁄ 2 inch (1435mm) gauge used by the CPRR equipment. The latter route was about twice as expensive per pound. Once the machinery and tools reached the San Francisco Bay area, they were put aboard river paddle steamers which transported them up the final 130 miles (210 km) of the Sacramento River to the new state capital in Sacramento. Many of these steam engines, railroad cars, and other machinery were shipped dismantled and had to be reassembled. Wooden timbers for railroad ties, trestles, bridges, firewood, and telegraph poles were harvested in California and transported to the project site.

When did construction of the transcontinental railroad begin?
Stream-of-consciousness: To answer this question, we should know that: The Central Pacific broke ground on January 8, 1863.