How many 14ers did I climb?

C, 174 bytes

a[99],c,p,j,M,m;main(i){for(i=j=1;c=getchar(),~c;i++)c<11?a[i]=j++,i=0:c&4?a[i]=j:0;for(m=j;c=a[i++];c>a[i-2]?M-m>1&&c-m>1?M=c,m=j,p++:M<c?M=m=c:M:m>c?m=c:0);printf("%d",p);}

Requires a trailing newline in the input, otherwise +4 bytes.


JavaScript (ES6), 133 bytes

s=>[...s].map((_,i)=>(c=s[i%h*w+i/h|0])=="/"?++a>2&&(p+=!d,d=a=3):c=="\\"&&--a<1&&(d=a=0),w=s.search`
`+1,h=-~s.length/w,a=3,d=p=1)|p

Explanation

Since the specifications are not stated clearly, this makes a couple of assumptions:

  • The bottom line is the 14,000ft mark (so all positions on the grid are high enough to count as a peak).
  • The grid starts at (or ascending) the first peak (since it's at least 14,000ft high already as per previous assumption).
  • A separate peak counts only after descending 300ft then ascending 300ft.

Iterates over the character c of each column (specifically, it iterates down each column until it finds a character). The current altitude is stored in a. It is clamped to a minimum of 0 and a maximum of 3. The direction needed to move to count the next peak is stored in d (false = up, true = down). If a reaches 3 and d is false, the number of peaks p is incremented and d is set to true (down). Once a reaches 0, d is set back to false (up).

var solution =

s=>
  [...s].map((_,i)=>   // loop
    (c=s[i%h*w+i/h|0]) // c = current character (moves down columns)
    =="/"?             // if c is '/'
      ++a>2&&          // increment a, if a equals 3 and d is true:
        (p+=!d,d=a=3)  // increment p, set d to true, clamp a to 3
    :c=="\\"&&         // if c is '\':
      --a<1&&          // decrement a, if a equals 0:
        (d=a=0),       // set d to false, clamp a to 0
    
    // Initialisation (happens BEFORE the above code)
    w=s.search`\n`+1,  // w = grid width
    h=-~s.length/w,    // h = grid height
    a=3,               // a = current altitude (min = 0, max = 3)
    d=                 // d = required direction (false = up, true = down)
    p=1                // p = number of found peaks
  )|p                  // output the number of peaks

var testCases = [`
/\\
`,`
/\\          
  \\         
   \\    /\\  
    \\  /  \\ 
     \\/    \\
`,`
\\    /
 \\  / 
  \\/  
`,`
            /\\            
         /\\/  \\/\\         
      /\\/        \\/\\      
   /\\/              \\/\\   
/\\/                    \\/\\
`,`
  /\\__/\\
 /      \\
/        \\
`,`
   /\\    /\\   
  /  \\  /  \\  
 /    \\/    \\ 
/            \\
`,`
   /\\      /\\   
  /  \\/\\  /  \\  
 /      \\/    \\ 
/              \\
`,`
         /\\___/\\_             
        /        \\    /\\      
       /          \\  /  \\     
   _/\\/            \\/    \\    
  /                       \\   
 /                         \\  
/                           \\_
`,`
                  /\\    /\\
         /\\      /  \\  /  
  /\\    /  \\    /    \\/   
 /  \\  /    \\  /          
/    \\/      \\/           
`,`
       /\\                 
 _/\\__/  \\                
/         \\               
`,`
      /\\                  
     /  \\   /\\            
    /    \\_/  \\           
   /           \\          
  /             \\         
 /               \\        
/                 \\       
`,`
              /\\          
    /\\_/\\    /  \\_        
   /     \\  /     \\     /\\
  /       \\/       \\   /  
 /                  \\_/   
/                         
`];
result.textContent = testCases.map(c=>c+"\n"+solution(c.slice(1,-1))).join`\n\n`;
<textarea id="input" rows="6" cols="40"></textarea><br /><button onclick="result.textContent=solution(input.value)">Go</button><pre id="result"></pre>