There were three ways to get from California to Washington D.C. at the time California became a state in 1850. The most direct route was overland, by wagon train, mostly via the Oregon Trail. This was also the slowest.

The second way was taking a steamship around the horn of South America. This was the most indirect route but still considerably faster than the overland route. But it was still dangerous and long, due to the rough waters south of South America.

The third way to go was to take a steamship to Panama, then disembark, travel by horse or mule-drawn wagon about twenty miles to the Chagres River, catch a riverboat to another steamship that would take you the rest of the way. This was the shortest and the least arduous, though of course it was still quite long. The trip across Panama itself could take 5 or more days, and each ocean voyage by steamship took at least a week, so the journey took 3 or 4 weeks total, depending on how long of a "layover" you had at each point along the way.

The first senators from California were John C. Fremont and William M. Gwin, who took the Panama route in early 1850. The Washington D.C. newspaper the Daily Union reported on February 12, 1850:

"We have had the pleasure of seeing Dr. William M. Gwin, one of the elected senators of California, who arrived in this city [Washington, D.C.] on Sunday morning last.

"Col. Fremont, the other senator, is unfortunately detained by the indisposition of his lady. Dr. Gwin left them at Panama."

By 1855, the Panama Railroad was complete, which made the trip a bit easier. It was then a matter of catching a steamship to Panama, boarding an overland train that took less than a day, and then catching the steamship on the other side.

For more information, this article published by the California Society of Pioneers gives some details as well as titles and info on many travel journals to and from California in the pre-Transcontinental Railroad era.

One of the most relevant is the book Mountains and Molehills: or, Recollections of a Burnt Journal by Frank Marryat, an English immigrant to California who arrived for the Gold Rush in 1850 via the Panama route. He, of course, was going the opposite way as the California senators were going, but the book opens with Marryat describing the town at the mouth of the Chagres River in Panama coming into view, and then him traversing the country to get to the Pacific Coast. It was rather haphazard, with both Native Americans and U.S. expatriates being involved in the accomodations and travel. About halfway along the route he stayed at the "Washington Hotel" operated by a "Yankee" that wasn't much more than a wood hut. Once arriving in Panama City, he described:

"Since Panama has become the half-way resting- place of Californian emigration, the old ruin has assumed quite a lively aspect. Never were modern improvements so suddenly and so effectually applied to a dilapidated relic of former grandeur as here. The streets present a vista of enormous sign-boards, and American flags droop from every house. The main street is composed almost entirely of hotels, eating-houses, and "hells.""

I don't know what a "hell" is that he's describing, but it doesn't sound good. In any case, this travel route seemed to be the most popular until the building of the Transcontinental Railroad.

It was, indeed, extremely hard for members of Congress to represent Western states and to return to run for re-election. This resulted in long sojourns in the East and difficult trips back and forth. Most of what I have seen had members of Congress returning to the West Coast by ship - usually taking the road across Panama and hitching on another ship north. (The Journals of Alfred Doten, 1849-1903, describe the comings and goings of these politicians, and invariably, they arrived in San Francisco by ship - and it was always noteworthy because it was so rare.) That took a lot of time, so it was not surprising that senators and representatives spent a long time in Washington, D.C. and returned rarely.

Even with the transcontinental railroad in 1869, the trip was not easy, so there was a lot more lingering in the capital than what one sees today.

Then there were those members of Congress who spent little time in Washington, D.C.: single-term U.S. Senator William Sharon (1821-1885; serving 1875-1881) is often credited with being the worse U.S. senator in history simply because of his remarkably poor attendance, missing over 90 percent of the votes during his six year tenure. As an added insult, he spent most of those years in California - even though he was representing Nevada! And all of this happened despite the fact that the railroad offered him transcontinental transportation. He simply didn't care.

There were, however, some excellent representatives from the Western states, but they needed to face the reality that visits home - if they were doing their jobs - would not occur very frequently.

It's worth noting that Senators weren't directly elected until the 17th amendment passed in 1913. I suppose this gives me a natural follow up: did Senators run campaigns for (re)election to persuade the state legislators to give them their job (again) prior to the 17th amendment?