On Feb. 8th, 1912, the first eastbound US transcontinental flight landed in Jacksonville, FL. After several Google searches, I can't find anything that says where the flight departed from. So where did it depart from?
The reason why your source does not give the starting location (Los Angeles) is because it took him months to do it due to weather and other delays, so the arrival notification just included the final legs:
The Brooklyn Daily Eagle Almanac, 1912
Robert G. Fowler (Wright Model B), started from San Francisco for New York Sept. 11, 1911, reaching Colfax, Cal. A second start was made from Los Angeles Oct. 18, and on Dec. 7, 1911, had reached Orange, Tex., a distance of 1,679 miles, measured in straight lines between towns, having been on his way 51 days.
FOWLER COMPLETES TRANS-CONTINENTAL FLlGHT
Robert G. Fowler, the second aerial transcontinental tourist, finally arrived at the Atlantic Ocean, at San Pablo beach, Fla., on Feb. 17, after having been 122 days on the way. A great deal of this time was consumed by reason of bad weather. The course followed was southerly all the way, close to the Gulf of Mexico through the extreme southern states to the coast.
Up to Jan. 11, at Biloxi, Miss., his mileage was 2,081, in straight lines between towns. Rodgers' flight was 3,391 miles. From then to February 17, he flew 436 miles in eleven stages. His itinerary follows:
Jan. 16, Evergreen, Ala., 84; Jan. 17, Georgiana, 17; Andalusia, 25; Jan. 20, Brantley, 22; Jan. 25, Troy, 23; Feb. 6, Bainbrldge, Ga., 106; Feb. 7, Thomasville, 38; Feb. 7, Qultman, 27; Feb. 8, Jacksonville, Fla., 82; on Feb. 17, he flew to Pablo Beach, 15 miles.
Fowler was dispatched all along the Seaboard Airline Railroad the same as a passenger train; and his manager Charles L. Young was posted every few moments in this way. As soon as Fowler was announced to be within 17 miles of the City of Jacksonville everyone seemed to loose their every thought of business, and spent the few moments watching for him to put in an appearance. When he was finally sighted at 4.30 the crowd at the Moncrief Race track seemed to go wild, and Aviator Max Lillie in his Wright biplane, dashed into his machine and flew away like mad to meet him he was immediately followed by Harold Kantner in his Moisant monoplane. The two aviators flew toward Fowler to greet him as best they could in the air. then circled Fowler, and escorted him toward the field. Lillie landed first to show Fowler the way. Fowler then circled the field 3 times and gave several dips and spiral dives that made the crowd stand up and yell with all their might. He then landed and was followed by Kantner. Fowler had been in the air but 90 minutes but it was a very cold day and he was almost frozen. After being given a right royal reception he was escorted to an automobile and rushed to the Seminole hotel where he was made the guest of honor. The evening was spent in trying to make Fowler feel at home, and he was given the key to the city and told to go as far as he liked.