The Cañón del Río Lobos is a protected Natural Park (for info about it:
www.patrimonionatural.org/ren.php?espacio_id=4 ) so it might be a good idea to get in touch with the
casa del parque (Park House) to get info about the park itself and about (possible) restricted or forbidden areas on your travel date (if they existed). The web of the
casa del parque:
www.patrimonionatural.org/casas.php?id_casa=15
I've been looking at maps and wondering if the following is possible. Stop in San Leonardo. I could then take a taxi to Ucero. Ucero is right close to the beginning of the trail through the Cañon and goes by San Bartolomé. Information I see says that Ucero to Hontoria is 25 km.
You know about taxis from San Leonardo and its fares and you know about accommodation in Ucero so with the info you already have you can almost answer your own question. The only thing I can think that might make it not possible would be that your route crossed a forbidden or restricted area (on your travel date) of the Natural Park but I guess an email or phone call to the
casa del parque would -easily- solve this doubt as well as any other about up to date access regulations to the Natural Park (because you never know when they can change them...).
BTW, you have to add another roughly 2kms from downtown Ucero to the point where the route starts what would make a total of 27kms.
And p.s., I've learned it's a 25 € cab ride from San Leonardo to Ucero, where the trail starts. I think it would be worth it, even though it will make me a cheater again.
If you want to walk it all, you have alternatives:
- To walk from San Leonardo to Ucero (21.7 kms), stay overnight in Ucero and walk next day from Ucero to Hontoria del Pinar. This option means roughly 8 kms of backtracking but, OTOH, you would see the ermita twice (once on your way to Ucero and another one on your way to Hontoria del Pinar). For info about the walk from San Leonardo to Ucero (on the GR86.2 and on the GR86): www.caminosoria.com/naturaleza/rutas-verdes/1699-gr-86-san-leonardo-ucero.html
- A variant of the alternative I quoted as 1 would be to walk from Navaleno to Ucero. In that case, you would miss San Leonardo. For info about the walk from Navaleno to Ucero (all of it on the GR86): www.caminosoria.com/naturaleza/rutas-verdes/1698-gr-86-navaleno-san-leonardo.html from Navaleno till the point where the GR86.2 meets the GR86 and the link I provided above from that point onwards.
- To walk from either San Leonardo or Navaleno to Casarejos (roughly 7 kms from S. Leonardo), stay overnight in Casarejos and walk next day from Casarejos to Hontoria del Pinar. From Casarejos to Hontoria del Pinar, you would follow the GR86 from Casarejos to the ermita. Once on the ermita, you would follow the track you linked in the OP till Hontoria del Pinar. Overall, Casarejos to Hontoria del Pinar following this route would be roughly 29 kms. This option means a backtracking of roughly 2 kms. It also means missing the route from Ucero to the ermita. In Casarejos, there's, at least, a posada and a casa rural but check fares beforehand to see if they are within your budget.
P.S.: I think I recall your travel companion on the camí català this year visited the ermita once ago? If memory serves me right (and she was there), she could provide you some info about it too.
P.S. (2): For some unkown reason, I don't get alerts when I'm mentioned on a post so, right now (i.e.: meanwhile the bug is detected and fixed), if you want to make sure I see a mention on a thread in which I didn't reply previously, the best way would be sending me a PM.