The original Los Angeles area interurban lines were 42" gauge. Los Angeles to Pasadena, Los Angeles to Santa Monica via Hollywood, and Los Angeles to San Pedro. Later these were all converted to standard gauge.

And the 3' gauge steam road Los Angeles & Redondo converted in 1902 to 42" gauge electric. It choose 42" gauge to allow it to run on the city system into downtown. With the 1911 consolidation, the LA&R was divided between the Los Angeles Ry and the (new) Pacific Electric; the inner portion went to the 42" gauge city system and the outer portion was standard gauged.

Thank you for the information about the Los Angeles interurban routes. I don't know much about that system. Did they operate with cars that were later standard-gauged, or were these retained as streetcars on the city system?

I am aware that many interurban cars were narrow due to space limitations. My eye just said the Peninsular car seemed narrower than most others I had seen. I looked at the PNAERC, out of curiosity, to see how the Peninsular cars ranked as far as narrow width preserved standard interurbans. Not including smaller "suburban" cars, there are very few standard interurban cars preserved that are so narrow and long as the Peninsular cars (Which are 8' 3" wide and 47' 6" long):

Elmira Corning & Waverly #107, Jewett-1911, New York Museum of Transportation, Rush NY (8' 3" wide and 46' long)
Montreal and Southern Counties #104/#107, Ottawa-1912, Canadian Ry Museum/Halton County (8' 4" wide and 49' 4" long)
Montreal and Southern Counties #610, Ottawa-1922, Seashore, (8'4" wide and 55' long)
Montreal and Southern Counties #611, Ottawa-1917, Canadian Ry Museum (8'4" wide and 55' long)
There are no cars 8' 5" wide, but quite a few that are 8' 6" wide (most of those are from properties in Ohio).

The PNAERC list also shows the Peninsular Ry cars are about a foot taller than similar cars in its width class. With a body that measures 13' 5" tall, it would be the same as a South Shore interurban, or the Columbus Delaware and Marion parlor at ORM. The height enhances the narrow appearance of these cars.

The supposed narrow gauge connection is an interesting anecdote, but I agree that it could be challenging to find any proof that the Toledo & Ann Arbor Electric Railway Company might have ordered narrow gauge interurban cars from American Car Company between 1901 and 1903, per the link mentioned earlier in this thread. The company appeared to have run out of funds at the end of 1903 after purchasing ROW, doing a survey, and grading the line. The web article did not mention ordering cars.

It was refinanced as Toledo, Ann Arbor and Detroit Electric Railway Company in 1905 and continued construction. It was interesting to me that this company (presumably still narrow gauge) had actually ordered interurban cars from the Niles Car Company. Shenanigans with the contractor's budget and a lawsuit from his wife apparently killed this project in 1912, though the line was mostly built.

And this is what I find interesting! Is it possible that the TAA&D Niles cars are the same that were used on the Twin Mountain and Potomac, a 3' gauge 16-mile shortline that was in West Virginia? This was discussed previously at RYPN:
http://www.rypn.org/forums/viewtopic.php?f=1&t=40857&p=263298

The TM&P was relatively late to the narrow gauge scene and was built to haul apples to market. Improvements to the railroad were made by a board member, Sylvanus Watson, who also had interests in various interurban properties. Presumably, that is the reason the passenger fleet was composed of short narrow cars built by Niles around 1912. The line only lasted until 1919 and equipment was transferred to a logging railroad in Orange, Virginia, which was called the Rapidan Railroad. When that line folded in 1926, two cars went to the Linville River Railroad, and served on the Tweetsie as well. So here, finally, is your narrow gauge interurban connection? Perhaps. It would be nice to see if one of these Niles carbodies were incorporated into someone's home or fishing lodge and survived to preservation.