Each trip from the Atlantic to the Pacific took around ten days.
1860
The Pony Express operated from April 1860 to October 1861 from St. Joseph, Missouri to Sacramento, California.
It wasn't overnight delivery, but it was fast. Ten days fron St. Joseph to San Francisco was like instant messaging compared to the normal six week journey for a letter.
People who rode the Pony express ran the horses as fast as they could all the way to the checkpoint. The horses that pulled Stagecoaches walked which made them slower than the Pony Express. There were no boats with engines when the Pony Express was around so boats moved slower and faster depending on the weather and it all had to be done by hand.
I really wouldn't say that the pony express was the beginning of communication in the 1860's they had mail delivery to the West long before the pony express it just took longer since it had to travel by ship or by stagecoach which could take about a month.. If your teacher is trying to state it was... then you should clarify if for him or her... Now the Pony Express was a rely system that cut the delivery time to about 10 days total... first the mail was sent by telegraphic communication (Morse code) covering about half the distance across the US and a the Pony Express carried it the rest of the way.
One impact was that when the telegraph line was completed from Saint Lewis to San Francisco, the Pony Express System along the same route had to shut down as the telegraph could send a message almost instantly that took the Pony Express 10 days to carry at a tiny fraction of the cost.
To make communication "easier" although it took a very, very long time to send letters.
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For the time, it was exceptionally fast and it was reliable. It was also very expensive at $5 per half ounce (about $85 for a one page letter) which meant that the market for such a service had no growth potential. There was also no possible way to make the service any faster. The telegraph took over the market once the line was completed and it was faster and much cheaper.
Between St. Joseph Missouri and San Francisco California.
Usually a day or two hence the name express mail. but my grand parents sent me something express and it took 3 days, so between 1-3 days