A California-based Christian radio network is using the Internet, thousands of billboards and even RV caravans to warn of overwhelming evidence that Judgment Day will arrive May 21.

The message is being spread by Family Stations, a 53-year-old non-profit, non-commercial, Christian radio network with 66 outlets. The billboards -- 1,200 in the USA and 2,000 worldwide -- do not mince words, promising in splashy colors: "The Bible guarantees it!"

The prediction says the world will be rocked by great earthquakes beginning at 6 p.m. ET and continue through Oct. 21. Believers will be called to the heavens.

Watch the The Newark Star-Ledger's interview with a businessman who is a believer but has had a hard time convincing his wife of 45 years.

The Orlando Sentinel reports that Family Radio has sponsored five caravans of followers who have traveled the country since October passing out leaflets about the big day.

Here are some key excerpts from the FAQ portion of the network's press packet:

What signs precede the Day of Judgment?

Jesus warned of several spiritual signs, such as the complete degradation of the Christian church, the devastating moral breakdown of society, the re-establishment of National Israel in 1948, the emergence of the 'Gay Pride Movement', and the complete disregard of the Bible in all of society today as direct evidence of His return. What if May 21 ends and nothing occurs?

The biblical evidence is too overwhelming and specific to be wrong. Christ's people can look with great confidence to this date because God promises His "beloved" He will not come upon them as a thief in the night.

God in His mercy has revealed the vital information needed to know the day. Judgment Day on May 21, 2011, will occur because the Bible declares it. Anyone whom God has not saved will arrive at that day with no hope for salvation. God warns simply the "door will be shut."

As to what qualifies Harold Camping, 89, the network's president and general manager, to make such a huge pronouncement, Family Radio notes he "has been a tireless student of the Bible for over five decades. The tens of thousands of hours he has spent analyzing the Bible has given him a unique perspective of the entirety of Scripture."

The Sentinel reports that Camping, who has a degree in civil engineering, and his followers cite Genesis, which says the flood began on the "17th day of the second month," as key to predicting the approaching Judgment Day. Camping says that translates into May 21, according to his interpretation of the Jewish calendar.

The newspaper notes that about 17 years ago, Camping warned of an apocalypse taking place Sept. 6, 1994. He says he had not completed his biblical research at the time.