Im pretty sure its located between the anus and genitals, on the opening the watchtowers section of JoS Maxine states that the chakra at the base of the tailbone is just the rear extension it seems to house the serpent so its a "unique" chakra extension and thus more powerful and very important much like how the third eye is an extension of the sixth chakra yet has unique properties, I may be wrong but repeatedly on JoS it is stated the chakras are located in the center of the body and the rear extensions are along the spine so I dont know why the base chakra would be an exception I may be wrong but I have researched this a lot lately and unless the info is out of date JoS I think its between the genitals and anus but I will say JoS does seem to present conflicting information regarding the location of the base chakra and it would be good for a guardian or priest/ess to provide clarity because even on the forums there's a different answer to this question each time its asked as I have researched it a lot.