Lhatsè-drak (lha rtse’i brag) literally means the Rock of Lhatse (Lhatse is a district in upper Tsang). Gayādhara and Drokmi ('brog mi) met and resided at Lhatsè-drak, where the former had a meditation cave. The Chronicle of Tibet explains that the time they spent there came to be known as the ‘month of Dharma’ as a result of their exchanges (Davidson, 166).
Lhatsè-drak appears only once in the Blue Annals. Interestingly, the Blue Annals indicates that Drokmi resided at Lhatsè-drak, where he "revised the translation of the Abhisamayālaṃkārakārikāvṛtti-śuddha-mati-nāma, chiefly propagated the Tantric doctrines and expounded numerous texts," but the site is not mentioned in the context of the initial meeting of Gayādhara and Drokmi (Roerich, 207).
Sources
The Blue Annals
Davidson, Tibetan Renaissance