Lank and J.C.'s tales of kilometres of new passages, including large tunnels, red stal and crystal pools, were at last able to fire enthusiasm in enough people for a large scale expedition in 1974. But of the 32 participants only 12 were members of MUSS. The others were from Bolton Speleo Club, ULSA, and John (Buddha) and Geoff Yeadon from Kendal Caving Club. These brothers were to be key figures in the expedition, among many other reasons, for their survey of Cubio de la Reñada. It's interesting, compared with later years, that not a single metre had been surveyed between 1970 and 1973.
Geoff began the exploration on 28th July by climbing an aven at the end of Cueva Tiva - a lead which was to be followed up in 1975. The first trip into Reñada was halted by heavy rain which sumped the duck at the end of the entrance series. But two days later, on 1st August, the level had gone down and exciting progress was made over the next few days through Castle Hall and Ghost Lake to discover the river passage, pursued upstream to Mega Hall and the sump. Squirrel's Passage was the river's downstream continuation. On 7th August work started on Lank and J.C.'s other great lead, Cueva Riaño, This was surveyed without any new breakthroughs, and in fact the length of 2.2km was less than J.C.'s estimate in 1973.
Other known caves were surveyed - Carcavuezo and Agua. The latter showed that the final sump was near to the resurgence at Cuevona, and on Wed. 14th August Geoff Yeadon made the connection by diving 60m from the resurgence to the cave.
The scaling-pole had been used without success in Cueva del Risco. But on 9th August, while expedition members were on a geological outing with Juan Carlos Fernández, a farmer showed them a new entrance. This turned out to be Cueva Oñite, and 1km was surveyed, at last connecting via a 20m pitch into Sala Carballo in Cueva del Risco. The first through-trip was then done.
On 10th August another farmer pointed out the entrance shaft of Torca de la Cabaña. Over a series of trips the pitches were descended and the large passages explored. Hopes were high for a connection with Reñada but despite dropping several pitches, including one of 60m, this was not to be.
Lank remembered the entrance he'd seen in 1970, and the exploration of Cueva Uzueka began on the 15th August, fiesta day in Riaño. Most of Quadraphenia was run through, halting at the sump beyond Pig's Trotters Chamber. The Flashbulb Hall area was also explored and photographed using large PF100 bulbs.
A final new cave was Cueva de Mortiro. On the 18th August this was explored upstream from its resurgence near the River Asón, through a free-dived 3m sump, to the top entrance in Hoyo de Mortiro.
The expedition was a complete success. In less than a month 16km had been surveyed. It had been an enjoyable experience in every way, particularly in the contact with the villagers. A Matienzo v. England football match was played, and a report appeared in "Alerta" newspaper - written by Jesús Aja, who'd taken part in the SESS expeditions. This success was added to by Buddha's rapid production of the expedition report, getting it ready for the BCRA conference in September.