Mynydd Hendre-ddu

{{Use dmy dates|date=April 2022}}

{{Infobox mountain

| name = Mynydd Hendre-ddu

| photo = Forest road on Mynydd Hendre-ddu - geograph.org.uk - 1453565.jpg

| photo_caption = Road on the flank of Mynydd Hendre-ddu

| elevation_m = 379.5

| elevation_ref = {{cite web|url=https://getoutside.ordnancesurvey.co.uk/local/mynydd-hendre-ddu-gwynedd |title=MYNYDD HENDRE-DDU, GWYNEDD (SY20 9LX) |access-date=7 September 2019 |publisher=Ordnance Survey}}

| prominence_m =

| prominence_ref =

| parent_peak =

| listing = Hendre-ddu mountain

| language = Welsh

| pronunciation =

| location = Gwynedd, UK

| range = Snowdonia

| grid_ref_UK =

| topo =

}}

Mynydd Hendre-ddu or Mynydd Hendreddu is a mountain in southern Snowdonia, Wales. It is one of a line of mountains running from Mynydd Dolgoed in the north, through Mynydd Llwydiarth to Mynydd Hendre-ddu and on to Mynydd y Foel, Y Grug, Mynydd Tri-Arglwyd and Mynydd Gwyn to the south of the village of Aberangell. It forms the watershed between Nant Llwydiarth, which flows to the south-west and into the Afon Dulas, and streams flowing into Afon Angell to the north, which flow east into the River Dyfi.

File:Disused quarry, Dyfi Forest - geograph.org.uk - 1453578.jpg

The summit is notable for a set of parallel ridges about {{convert|80|cm|in}} across and {{convert|130|m|ft}} long that run across it.{{Coflein|num=400825 |desc=Mynydd Hendre-ddu, Ridges (?natural Feature) |access-date=29 September 2021}}

On the northern slope of the mountain lay the Hendreddu quarry which was connected to Aberangell by the Hendre-Ddu Tramway.

Mynydd Hendre-ddu is one of the Dyfi hills.