Summary
In mid-July of 1805, the expedition had still not sighted
any Indians, although  signs of their proximity proliferated.  Soon,
Sacajawea informed the expedition  that they were in Shoshoni territory;
she had noted and identified markings  and abandoned camp sites.
 At this point, both Captain Clark and  Charbonneau had fallen extremely
ill.  It was now crucial that the  expedition increase their rate
of travel if they were to reach the Pacific  before winter; but
this would not be possible without horses; an only the  Shoshoni
people could supply the animals.
Now in Shoshoni territory, the expedition came to the
spot where Sacajawea  remembered being captured by the Hidatsas
at age twelve; on August 11, 1805,  the expedition finally came
into contact with its first Shoshoni, a warrior  wandering alone.
 Lewis made a gesture of peace by laying a blanket on the  ground,
and the warrior approached.  However, threatening movements by Lewis'
 subordinates scared him off.  This did not bode well for establishing good
 relations with the Shoshoni, or for acquiring horses.  Luckily, the
expedition  had Sacajawea with them.
On August 13, the party met a group of Shoshoni women
who, because they had  children with them, were unable to run away quickly.
 They expected to be  killed, but Lewis and Clark surprised them
with presents instead.  The women  then led the expedition to the
Shoshoni camp, where they exchanged more gifts  and smoked pipes.
 (This was before Clark and Sacajawea made it to the camp; the 
captains had divided the expedition members between them and had
been patrolling  separately; Sacajawea had been in Clark's group.)
Most of the presents Lewis and  initially gave to the Shoshoni were
Jefferson medallions, depicting the face of  this man the Indians
called the "Great White Chief."  The Shoshoni chief,  Cameahwait,
treated Lewis and his men with kindness, though most of the  other
Indians feared the white men.
When's Clark's group made it to the Shoshoni camp, Sacajawea was
overjoyed.   After all, she had been separated from her people since
early girlhood.   Clark noted that she danced happily when she saw
that a Shoshoni party was  approaching them.  Sacajawea proved her
value as an interpreter, and surprised  everyone when she and Cameahwait
determined they were brother and sister.  
Initially, Cameahwait haggled and traded only a handful
of horses to the  expedition.  Lewis and Clark were very happy to
have three or four.  Later,  however, Cameahwait would relent and
give his sister's friends many more.  When  it came time to leave
the Shoshoni, Sacajawea did not stay, but loyally followed  her
husband and the Lewis and Clark expedition.
One of the major reasons the Lewis and Clark Expedition
went so long without  meeting any Shoshoni was that Sacajawea accompanied
them.  If this woman  carrying a baby had not been present, the Shoshoni
might have perceived the  white men as a threat and attacked them
before they could come too close to  their village.  But Sacajawea
and her child marked the expedition as peaceful.   Moreover, the
Shoshoni of this region were themselves a peace-loving people. 
  Instead of guns, they still used bows and arrows.