The following entry is typical of the more than 2700 entries in Monterey County Place Names. It's for Jolon, in southern Monterey County. It's a good example of why it's often difficult to pin down the source of a name. And, it shows the kind of job a good researcher can do.
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Jolon A small settlement about 20 m SW of King City at the junction of Jolon and Mission roads 3 m SE of Mission San Antonio de Padua in Sec.35 T22S R7E. Jolon was the site of an Indian village at the time of the Portolá expedition in 1769. Its beginnings as an American community go back to 1850 when Antonio Ramirez came from Monterey and built an adobe inn which later became known as the Dutton Hotel (q.v.).

Jolon is an aboriginal site of Salinan Indians (Kroeber); the meaning of the name is ‘valley of dead trees,’ according to Paul Parker. Bancroft shows the name of the locality near San Antonio Mission on his map (1885) of the Monterey District as it existed in 1801-1810 (II,145). Cañada de Jolon is recorded on a diseño of the Los Ojitos grant (1842). The name does not seem to appear on early American maps, but Jolon ranch and a post office are mentioned by Brewer, May 8, 1861 (p.93). — Gudde 1969:195.


 

Mellini (1979:25) reported that an entry in Antonio del Valle’s diary for 1824 contained "the first mention of Jolon by name in Spanish and Mexican records."

 

There have been many meanings attributed to the name Jolon:

 

1911: This is an Indian word, spelled according to the Spanish pronunciation. The writer heard two meanings of the word: one, that it signifies a resting place; the other, a place where bulrushes grow, that is, a place that one would be apt to select for a camping spot, as yielding water, which comes, after all, pretty near the first meaning. Who gave it that name, and whether it was derived from the old mission Indians, the writer was unable to learn. — Carter 1911:104-105.

 1916: Jolon, in Monterey County, is an aboriginal site of the so-called Salinan Indians, and is still inhabited by them. The origin of the name, however, is uncertain, and the meaning undetermined. — Kroeber 1916:44.  

1922: A word of doubtful origin, which has been variously explained. It is thought by some persons to be a corruption of Jalón, a personal name, but old Spanish residents say it is an Indian word, meaning ‘valley of dead oaks.’ — Sanchez 1922:159-160.

 1925: Holamna´– the vicinity of Jolon, meaning an arroyo; and tcau´temmak — the site of Jolon, meaning "where there is plenty of cattle." — Mason 1925:108, citing Henshaw.  

1925: Jolon: According to local tradition an Indian name meaning "Valley of Dead Oaks." — Rider 1925:309.

 1925: Jolon. Probably Salinan. — Kroeber 1925:895.  

1926: Jolon. Indian valley of Dead oaks, or "snow." — Mott 1926:36.

 

1932: xóllom’. Harrington 1932:reel 88:635 reported that his informant, Felipe, stated that Jolon came from the Indian word xóllom’ which means "a cienega or something that is dammed up and suddenly breaks through."

 1932: hólom. Harrington 1932:reel 87:731 reported that his informant, Dave, stated that Jolon came from the Indian word hólom which means "it has a leak in it, for example a dish has a leak in its bottom."  

1970: Jolon. Salinian, perhaps ‘valley of dead trees.’-Stewart 1979:229.

 1975: There were several meanings of Jolon. First one I read of, in very old writing, said it meant ‘meeting place.’ Later, a meaning was ‘place of a leak.’ Then in Mission days,‘place of much cattle.’ Still later ‘place of dead oaks.’ - Letter to JDJ from Olive Wollesen, July 30, 1975.  

1975: [In a listing of Indian and early Spanish names of the San Antonio area sent to JDJ in September 1975 Valence Heinsen wrote]: Holomna: the first Portola expedition Spanished the village Jolon. The villagers were probably out to meet the expedition having had prior knowledge of it. They met at the San Antonio River though their village was in a terrestrial pocket which was the site of native pow-wows in favorable seasons. And this is the correct translation of the word Holomna. Since pow-wows depended upon the favorable season when they, the pow-wows, were ended the season was passed and thus we have "dead trees" which is a common though erroneous translation for Holomna. Being an oriental word Holomna was subject to various meanings. Henry Yates, who is a descendent of Carmel Indians, agrees with the "terrestrial pocket" translation. It was also carried forward by the Poison Oakers, that is the natives of the coastal ravines.

 1976: Jolon: The site of an Indian village at the time of the Portola expedition in 1769, became the nucleus for a town in 1850. The origin of the name is in dispute, no one seeming to know it for certain. Although the Indians of the San Antonio area are referred to in histories as Salinans and Mutsons they are locally called Jolon Indians. — Casey 1976:58.  

1979: Jolon or "Holomna" translates variously to English as water source, places of dead trees, and meeting place. — Mellini 1979.

 

1985: It seems to me that the Indian word Jolon may have had something to do with the tules. Tules are cat tail rushes, or reeds, which grow only where the water stands continually in shallow places. The Indians made good use of tules for every day chores. Ajole means tules. There was a place called Jol, an Indian village location, called El Tule at the mission, and is still known as "The Tule." It was a swampy place with cat tails until deep wells were used there, nearby.…[L]ong ago there were boats over on the coast that were called "Jolons." Were those boats made of rushes from Jolon? Is there a connection in the name’s usage?

 It seems to me that the native people, as times changed, did not change the name "Jolon" but they only described the change of circumstances at the place. At first, they said it was "the meeting place." Surely that was a good name. Even still, Jolon is like the hub of a wheel, with roads and trails like spokes in every direction. The meeting place.  

The Jolon was a "leak" as though some sudden torrent of water poured out of every canyon or stream.

The third description was "place of much cattle," and I’m sure it was just that.

 The fourth description was "place of dead trees." When the foreigners came in to gather the natives into the mission, they began to dam the stream for irrigation, to girdle trees so they would die and could be burned for clearing of land. I am not sure of these definitions. This is the way I see it. — Wollesen.1985:1.  

1990: Jolon…said to be an Indian word for "valley of the dead oaks." — Hoover 1990:221


And then, there is this bit of folklore:

 
 Popular story has it that the road approaching the village had a very steep and difficult pitch and that everyone on a stage or wagon would yell "hold on," which became corrupted into the name "Jolon." — p.c., JDJ from Sheriff William A. "Jack" Davenport July 16, 1974.  
  

Don Howard offers a variation of the "hold on" story:

 
 An amusing but erroneous account of the origin of the name "Jolon" is told in southern Monterey County. Two teamsters on a stage were pulling into the Dutton Hotel one day in the 1880s, the story goes, when one of the horses reared and became unruly. In an effort to control the uncooperative animal, the driver madly shouted "hold on" until the valley echoed with the phrase. — Don Howard "Jolon — An Introduction" in Monterey County Archaeological Society Quarterly, Vol.4, No.2, Winter, 1975.  
 

Ref: In addition to the references given in the text see Paulson 1875:254; Elliott 1881:77; Salt 1951:3; Herald Weekend Magazine, July 29, 1972; Heinsen 1975:9-10; Wollesen 1985

 

Map: 1877COX, 1881ELL, Bancroft 1886:II:145, 1892SAN, Hamlin 1904:10, 1908RAN, 1908USF, 1910REC, 1911HAR, 1915SPC, 1919BRY, 1919COZ, 1920HIG, 1925MON, 1926CRC, 1941USA sheet #14, 1947ACS, 1949JOL, 1970SPO, Pearson 1984:maps A & M, DeLorme 1986:44, Thomas 1987:6 as Jolon; Rough Sketch Map of the Rancho "Los Ojitos" August 6, 1858 in Book of Deeds C:447 as Jolon o Culon also shows house of Anto. Ramirez; Heinsen 1975:8 (map of Jolon as of 1911); 1892MAS as Jelon; Kroeber 1925:548 as Holamna; 1866ALL, USS-T22S-R7E 1859-1883 show location of Ramirez’ house