1666: cave
Riaño 30T 452778 4799391 (Datum: ETRS89. Accuracy code: M) Altitude 306m
Length 46m
Area position

Updated 2nd November 2002; 18th February 2012; 30th April 2016

   One of the small resurgence caves that feeds the sink at site 1618 about 80m above 4th River Inlet area in Hoyuca. The other resurgence is site 1617.
   A small, draughting entrance at the top of a tiny, overgrown streambed drops straight into a hole with a hands and knees crawl at roof level. Water is then met , followed by a short crawl over a mud false floor, another watery section and a step to the left. After another 8m, exploration has temporarily ended at another mud false floor with a wet crawl underneath. The passage can be seen to continue for at least another 10m.
   At Easter 2016, the cave was thought to sump a short way in with a mud bank acting as a dam at the entrance. A trench was dug to start draining the water.

The cave appears on the Cueva Hoyuca and the Four Valleys System Hydrology diagram.

Reference: anon., 2001c (Summer logbook); anon., 2002b (summer logbook); Corrin Juan, 2003a; Corrin Juan, 2003b; anon., 2016b (Easter logbook)
Entrance picture: yes  video of jungle and the entrance
Underground picture(s):
Detailed survey: 1:500
Line survey:
On area survey:
Survex file: yes (Amended magnetic declination December 2013 to align with Eur79 grid and coordinates altered to fit ETRS89 datum, April 2014.)
Hydrology (Terry Whitaker): Hoyuca and the 4 Valleys System

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