It is a blessed stony ground. Musa (one of the narrators) said: Salim made his came) halt at the mosque where 'Abdullah made his camel halt as seeking the place of stay of Messenger of Allah ﷺ. It is, in fact, situated at a lower plain than the mosque, which stands in the heart of the valley, and it is between it (the mosque) (and Qibla) that that place (where Allah's Apostle used to get down for rest and prayer) is situated. (Using translation from Muslim 1346b)
أَنَّ رَسُولَ اللهِ ﷺ أُتِيَ وَهُوَ فِي الْمُعَرَّسِ مِنْ ذِي الْحُلَيْفَةِ فِي بَطْنِ الْوَادِي فَقِيلَ إِنَّكَ فِي بَطْحَاءَ مُبَارَكَةٍ