The words to this 8 minute 45 second largely instrumental track are not as nonsensical as they may appear at first glance.
Zappa appears to have written "Inca Roads" in 1973, around five years after the publication of Erich von Däniken's Chariots Of The Gods. This book was followed by a plethora of similar books by sundry authors including R.L. Dione's God Drives A Flying Saucer and The Spaceships Of Ezekiel by the aeronautical engineer and NASA program developer Josef F. Blumrich.
Although the extraterrestrial hypothesis was soon largely discredited, it had and continues to have a profound influence on popular culture, including music, inspiring inarguably the greatest Christmas song ever written, "A Spaceman Came Traveling."
Although "Inca Roads" is not in that class, it does contain some fine jazz fusion, and as with many of Mr. Zappa's compositions, some of the lyrics are indeed nonsensical. The references herein to Ruth allude to Ruth Underwood, who played percussion for Zappa from 1967 to 1977, and who of course appears on this 1975 release.
"Inca Roads" includes some off-beat time signatures including 5/4 (as in "Take Five") and 7/8.
The song is also notable for having a skip in it, which probably most listeners didn't notice. It is the first track on the One Size Fits All album.
Suggestion credit: Alexander Baron - London, England, for above 3